John  3'.''ett 


. 


\ 


FIRST    BOOK 


PHYSIOLOGY 


FOB     THE     USE     OF 


SCHOOLS  AND  FAMILIES, 


INTENDED  AS  INTRODUCTORY  TO  THE  LARGER  WORK 
BY  THE  SAME  AUTHOR. 


BY  WORTHINGTON  HOOKER,  M.  D., 

PROFESSOR    OF    THE    THEORY   AB/>    PRACTICE    OF    MEDICINE  IN   TALE   COLLEGE; 
AUTHOR  OF  "  PHYSICIAN  AND  PATIENT,"    "  HUMAN  PHYSIOLOGY,"  ETO. 


ILLUSTRATED  BY  ENGRAVINGS. 

NEW   YOKE: 

PRATT,    OAKLEY    AND    COMPANY. 

NO.    4    CORTLANDT    STREET. 

1857. 


b"5 


ENTURKD  according  to  Act  of  Congress,  in  the  Year  One  Thousand  JSferht  Hundred 
and  Fifty-five,  by  WORTHINGTON  HOOKER,  M.  D.,  in  tho  Clerk's  Office  of 
the  District  Court  of  the  United  States,  for  the  District  of  Connecticut. 


JONES  &  DENYSE,  STEREOTYPERS, 
183  William-street,  New  York. 


PREFACE. 


THIS  book  is  intended  for  beginners  in  the  study  of  Physiology, 
of  whatever  age  they  may  be.  It  is  a  ". First  Book"  for  the  adult 
as  well  as  for  the  child.  There  is  more  in  common  between 
young  and  adult  minds,  in  regard  to  a  subject  which  is  new  to 
them,  than  is  commonly  supposed.  There  is  for  both  the  same 
need  of  simple,  clear,  and  precise  statement,  with  familiar  illus- 
tration. A  book  intended  to  instruct  a  child  in  any  science  should 
be  so  written,  that  it  will  be  just  as  instructive  to  an  adult  unac- 
quainted with  the  subject.  Not  o'nly  so,  but  it  should  be  so  written, 
that  it  will  interest  and  please  a  mind  that  has  a  full  knowledge 
of  the  subject,  by  its  logical  and  clear  development  of  simple  fun- 
damental facts  and  principles. 

It  is  a  common  error  to  suppose,  that  there  need  not  to  be  as 
logical  a  presentation  of  a  subject  in  teaching  children  as  in 
teaching  adults.  A  correct  logic,  in  the  true  sense  of  that  word, 
is  necessary  in  either  case.  In  teaching  any  science,  no  matter 
what  the  age  of  the  scholar  may  be,  a  natural,  that  is,  a  logical, 
arrangement  of  the  facts  and  principles,  is  essential  to  success. 
Indeed,  it  is  more  essential  at  the  outset  than  it  is  subsequently, 
for  the  beginner  lays  the  very  foundations  of  his  knowledge,  upon 
which  in  his  course  of  learning  afterwards  he  builds  up  the  super- 
structure. It  is  the  simple  facts  and  principles  of  science,  such  as 
should  be  taught  to  the  beginner,  that  are  fundamental.  In  order 
that  he  may  begin  right,  he  must  acquire  a  clear  idea  of  these. 


543486 


iv  PREFACE. 


This,  it  is  obvious,  cannot  be  done  by  a  loose,  partial,  and  ill- 
arranged  presentation  of  them,  but  only  by  a  presentation  that  is 
strictly  logical.  Commonly,  this  foundation- work,  as  it  may  be 
termed,  has  to  be  done  over  and  over  again,  bringing  much  unne- 
cessary labor  to  both  teacher  and  scholar,  simply  because  it  is  not 
done  right  at  the  outset. 

There  is  another  consideration  bearing  upon  this  point,  which  is 
of  great  importance.  It  is  essential  to  the  successful  study  of 
science  that  good  habits  of  mind  be  formed,  and  the  earlier  they 
are  formed  the  better.  I  need  not  stop  to  show  that  clear  logical 
presentations  of  facts  and  principles  tend  to  form  such  habits,  and 
that  a  loose,  confused  mode  of  presenting  them  tends  to  form  habits 
of  an  opposite  character. 

Let  me  not  be  understood  to  advocate  that  prominence  of  logical 
framework,  as  it  may  be  -called,  which  is  so  common  in  books  for 
instruction.  With  all  this  show  of  logical  arrangement,  there  is 
often  much  that  is  really  very  illogical.  With  the  beginner,  at 
least,  the  less  there  is  of  the  formalities  of  arrangement  the  better. 
And  yet  there  should  in  reality  be  a  strict  regard  to  the  proper 
logical  order  in  introducing  facts  and  principles  to  the  mind  of  the 
learner.  If  this  natural  order  be  observed,  every  page  that  the 
student  learns  serves  to  prepare  his  mind  for  what  comes  after. 
There  is  no  point  in  which  books  for  instruction  so  often  fail  as  in 
this. 

Most  books  for  the  instruction  of  beginners  in  science,  present  a 
strange  mixture  of  child's  talk,  and  language  that  the  child  cannot 
understand,  but  can  only  learn  by  rote.  Even  the  hard  technical 
terms  of  science  often  enter  abundantly  into  the  compound.  It 
seems  to  be  forgotten  that  great  simplicity  of  language  may  be 
the  vehicle  of  even  a  deep  philosophy,  and  is  consistent  with  an 
elevated  style.  Clear,  precise  statement,  logical  order  of  arrange- 
ment, and  felicitous  illustration,  are  the  elements  of  such  a  style. 
And  these  elements  cannot  exist,  unless  there  be  an  appreciation 
in  the  writer's  mind  of  the  attitude  of  the  minds  that  he  addresses. 
He  must  not  only  see  clearly  the  facts  and  principles  of  science 
himself,  but  he  must  know  how  to  make  others  see  them  clearly 
also. 


PREFACE. 


It  is  obvious  that  in  a  "  First  Book  "  there  must  be  a  less  num- 
ber of  points  introduced  than  in  a  book  intended  for  instruction 
afterward.  The  field  of  vision  should  be  gradually  enlarged  as 
the  learner  advances.  At  first  there  must  be  a  selection  of  such 
points  as  he  can  most  readily  understand,  reserving  the  more  diffi- 
cult ones  for  another  book.  And  while  the  second  book  should  be 
much  more  complete  than  that  which  is  designed  for  beginners,  yet 
im  the  latter  the  really  essential  and  fundamental  parts  of  the 
science  should  be  clearly  presented. 

The  principles  thus  advanced  I  have  endeavored  to  follow  in  the 
construction  of  this  little  work.  It  is  intended  principally  for  the 
use  of  common  schools,  and  yet,  like  my  larger  work  on  Physiology, 
it  is  adapted  for  general  reading.  It  will  prepare  the  reader  and 
the  scholar  for  the  more  full  examination  of  the  subject  in  the 
larger  work. 

I  need  hardly  say,  that  in  order  to  teach  from  this  book  satisfac- 
torily, it  is  necessary  for  the  teacher  to  read  both  books.  By  doing 
so.  he  will  see  clearly  in  every  case  the  reason  of  the  selection  that 
I  have  made  in  this  work  from  the  facts  that  are  presented  so  fully 
in  the  other,  and  will  therefore  be  better  prepared  to  teach  according 
to  the  plan  that  I  have  in  view.  The  questions  that  I  have  placed 
at  the  bottom  of  each  page  can  be  altered  as  the  teacher  thinks 
best,  to  suit  the  different  capacities  of  his  scholars.  For  certain 
general  directions  in  teaching  Physiology,  I  refer  him  to  the  Ap- 
pendix of  my  larger  work. 


CONTENTS. 


CHAPTER  I. 
THE  MACHINES Y  OF  THE  BODY       .        .       .       .       .       .      9 

CHAPTER  II. 
THE  DIFFERENT  STBUCTUKES  OF  THE  BODY    ...       14 

CHAPTER  III. 
DIGESTION         ..„.'«»„ 22 

CHAPTER  IV. 
CIRCULATION  OF  THE  BLOOD         .       .        .       .       .       .       86 

CHAPTER  V. 
EESPIKATION 64 

CHAPTER  VI. 
BUILDING  AND  KEPAIKINQ     .       .       .       „       .       •       .       74 

CHAPTER  VII. 
THE  NERVOUS  SYSTEM  .       . 94 

CHAPTER  VIII. 
THE  BONES     .        .       .       .       .    '  ,       ...       .       .107 

CHAPTER  IX. 
THE  MUSCLES  .       ...       .     ....       ...       .       .       .180 

CHAPTER  X. 
THE  EYE          .       ....       .       .       .       .       .       .      158 

CHAPTER  XL 
THE  EAK     .       .       .       .       .       .       .       .       .       .       .       .168 

CHAPTER  XII. 
CONNECTION  OF  THE  MIND  AND  BODY      .  180 


FIRST  BOOK  IN  PHYSIOLOGY. 


CHAPTER   I. 

THE  MACHINERY  OF  THE  BODY. 
• 

1.  WHEN  you  look  at  any  machine  made  by  man, 
you  inquire  what  it  is  intended  to  do.     You  find,  com- 
monly, that  it  is  for  some  one  purpose.     Thus,  a  nail- 
machine  makes  nails,  and  does  nothing  else  ;  a  paper- 
machine  makes  paper  ;  a  locomotive  draws  cars  on  a 
track  ;  and  so  of  other  machines. 

2.  But  the  human  body  is  not  a  single  machine  for 
a  single  purpose.     It  is  a  complicated  machine,  and 
serves  many  purposes.     It  differs  very  much  in  this  re- 
spect from  the  machines  that  man  makes.     While  for 
example,  it  is  a  machine  that  walks,  walking  is  not  the 
only  thing  that  it  does.     It  is  not  like  the  locomotive, 
that  does  nothing  but  draw  cars.     It  can  perform  a 
great  variety  of  motions  besides  walking.     It  can  run, 
jump,  leap, -climb,  &c. 

3.  You  see  the  same  difference,  if  instead  of  look- 
ing at  the  body  as  a  whole,  you  look  at  any  particular 
part  of  it.     Look,  for  example,  at  the  hand,  and  com- 

What  is  said  of  machines  made  by  man  ?     How  does  the  machinery 
of  the  body  differ  from  these  ? 
1* 


BO.OK   IN    PHYSIOLOGY. 


ingenious  machinery  that  man 
has  ever  made.  The  variety  of  things  that  it  can  do 
is  almost  endless.  So,  too,  if  you  open  your  mouth 
before  a  looking-glass,  and  move  about  that  busy  little 
machine,  the  tongue,  you  will  get  some  idea  of  the 
great  variety  of  motion  that  it  can  perform. 

4.  But  besides  being  a  locomotive  machine,  capable 
of  all  this  variety  of  motion,  the  human  body  is  also 
a  machine  in  which  many  things  are  made.     Blood  is 
made  in  it.     This  red  fluid  is  made  out  of  the  food 
which^his  machine  puts  into  its  mouth  and  eats.     And 
then  from  the  blood  are  made  all  the  various  parts  of 
the  body. 

5.  In  order  that  the  blood  may  be  used  to  construct 
all  parts  of  the  body,  it  must  be  carried  everywhere. 
There  is  a  wonderful  set  of  machinery  to  do  this.    The 
heart  is  pumping   night  and  day,  sending  out  the 
blood  through  the  pipes  that  branch  out  from  it  all 
over  the  body. 

6.  Then  the  blood,  when  it  has  been  used,  is  not  fit 
to  be  used  again  until  it  is  changed.     There  is,  there- 
fore, a  set  of  machinery  in  the  chest  for  the  purpose 
of  changing  the  blood.     The  blood  is  carried  to  the 
lungs,  and  there  it  is  exposed  to  the  air  that  we  breathe 
into  the  lungs  every  time  that  we  draw  a  breath.     By 
being  aired  in  this  way,  it  is  fitted  to  be  used  again, 
and  it  goes  back  to  the  heart  that  it  may  be  pumped 
out  again  all  over  the  body. 

7.  But  the  most  wonderful  machinery  in  the  body 

Mention  some  particular  parts  of  the  body  in  which  this  difference  is 
seen.  What  is  made  by  the  machinery  of  the  body  ?  By  what  ma- 
chinery is  the  blood  circulated  ?  How  is  the  blood  changed  after  it  hns 
been  used  ? 


MACHINERY   OF  THE   BODY.  11 

is  that  which  we  find  in  the  nervous  system.  The 
brain  is  the  great  central  organ  of  this  system.  From 
it  branch  out  white  cords,  called  nerves,  which  are 
found  in  every  part  of  the  body.  This  nervous  system 
is  somewhat  like  a  telegraph,  though  it  is  much  more 
perfect  and  mysterious.  The  brain  may  be  consid- 
ered as  the  central  office,  where  the  mind  has  its  seat. 
The  nerves  may  be  called  the  wires,  by  which  mes- 
sages are  sent  forth  and  received  by  the  mind. 

8.  Messages  are  sent  by  means  of  the  nerves  to  the 
muscles,  whenever  the  mind  wills  that  any  part  of  the 
body  move.     Thus,  when   you   wish   to   move   your 
hand,  messages  are  sent  from  the  brain  to  the  muscles 
that  move  this  part.     When  the  mind  wills  that  the 
whole  body  shall  move,  a  great  number  of  these  mes- 
sages are  sent  in  all  directions  at  once. 

9.  The  mind  too  receives  messages   through  the 
nerves.     It  receives  them  from  the  senses.     When 
we  see,  something  is  sent  by  means  of  the  nerves  of 
the  eyes  to  the  brain,  and  thus  reaches  the  mind,  just 
as  electricity  goes  along  the  wires  of  a  telegraph.  And 
the  same  may  be  said  of  the  other  senses. 

10.  Observe  now  how  great  a  variety  of  machinery 
there  is  in  the  body.     The  digestive  machinery  grinds 
up  the  food  with  its  teeth  and  mixes  it  with  juices  in 
such  a  way  that  blood  is  made  out  of  it.     Then  the 
machinery  of  the  circulation  moves  the  blood  about 
everywhere  in  the  body,  so  that  all  the  parts  may  be 
made  out  of  it  and  be  kept  in  repair.     The  breathing 

What  is  the  most  wonderful  machinery  in  the  body  ?  What  is  it 
like  ?  And  how  ?  Describe  what  is  done  when  the  muscles  act.  How 
and  from  what  does  the  mind  receive  messages  ?  Give  what  is  stated 
in  Tf  10  about  the  variety  of  the  machinery  in  the  body. 


12     ,         FIRST    BOOK   IN    PHYSIOLOGY. 

machinery  continually  purifies  the  blood  after  it  has 
been  used,  and  so  fits  it  again  for  use.  Then  by  means 
of  the  nervous  machinery  the  mind  uses  the  parts  that 
are  thus  constructed  from  the  blood — viz.,  the  mus- 
cles, the  bones,  and  the  organs  of  the  senses. 

11.  You  see  that  some  of  the   machinery  of  the 
body  is  for  the  purpose  of  making  other  machinery. 
This  is  the  business  of  the  machinery  of  the  digestion, 
the  circulation,  and  the  respiration.     This  machinery 
makes  nerves,  and  muscles,  and  bones,  and  the  brain, 
and  the  eye,  and  the  other  organs  of  the  senses.     The 
object  then  of  eating  and  drinking  and  breathing  and 
having  the  blood  circulate,  is  to  make  machinery  for 
the  mind  to  use. 

12.  There  is  one  difference  between  the  machinery 
of  the  body  and  the  machines  constructed  by  man,  that 
I  have  not  yet  mentioned.     When  man  makes  a  ma- 
chine he  cannot  use  it  till  it  is  completed.     If  he 
wishes  to  alter  it  or  repair  it,  he  cannot  use  it  at  all 
while  he  is  doing  this.     But  the  machinery  of  the 
l?€>dy  is  constantly  altered  while  it  is  in  use.     I  will 
illustrate  this  difference. 

13.  The  machinery  of  the  child's  body  is  small  ma- 
chinery, but  every  part  of  it  gradually  becomes  larger, 
and  in  manhood  it  is  of  its  full  size.    But  no  machine 
made  by  man  can  grow  to  be  a  larger  one.     Now,  the 
machinery  of  the  body  not  only  grows,  but  it  is  kept 
in  use  while  it  is  growing.     A  small  telescope  never 
grows  to  be  a  large  one,  but  the  little  eye  of  the  infant 

Can  the  machinery  that  man  makes  be  kept  in  use  while  he  is  altering 
or  repairing  it?  How  is  it  with  the  machinery  of  the  body  ?  What  is 
said  of  the  growing  of  the  machinery  of  the  body  ? 


MACHINERY    OF   THE   BODY.  13 

grows  to  be  the  large  eye  of  a  man,  and  is  used  every 
day  while  this  is  done.  A  cord  does  not  grow  to  be  a 
rope,  but  the  muscles  grow  as  we  use  them. 

14.  The  machines  that  man  constructs  cannot  be 
repaired  while  they  are  in  use  ;  they  have  to  lie  ~by  for 
repair,  as  it  is  expressed.     It  is  not  so  with  the  ma- 
chinery of  the  body  ;  repairing  is  going  on  while  it  is 
in  use.     In  the  machinery  made  by  man  it  is  done 
only  now  and  then,  but  in  the  machinery  of  the  body 
it  is  done  all  the  time,  every  day,  every  hour,  every 
moment. 

15.  One  thing  is  to  be  noticed,  however,  about  this 
repairing  of  the  body.     Some  of  its  machinery  must 
have  seasons  of  rest,  in  order  that  the  repairing  may 
be  thoroughly  done.     This  is  the  case  with  the  brain, 
the  nerves,  and  the  muscles.     When   the  mind  has 
worked  these  parts  of  the  machinery  during  the  day, 
the  rest  of  night  is  needed  to  repair  fully  the  wear 
and  tear.     Though  the  business  of  repairing  them  is 
going  on  all  the  time,  more  of  it  is  done  while  they 
are  at  rest  in  the  hours  of  sleep  than  when  we  are 
awake. 

16.  Another  thing  to  be  remarked  is,  that  when  the 
machinery  is  much  deranged  by  disease,  more  rest 
than  is  commonly  taken  at  night  is  needed.     There 
must  be  some  lying  by  for  repair  now.     Thus,  if  a 
limb  be  inflamed,  it  must  be  kept  still.     An  inflamed 
eye  needs  to  have  the  light  shut  out  from  it.     If  the 
brain  be  diseased,  the  mind  must  be  kept  from  using 

Does  the  machinery  of  the  body  lie  by  for  repair  ?  What  parts  of 
the  machinery  of  the  body  must  have  seasons  of  rest  to  have  the  re- 
pairing well  done  ?  What  is  said  of  the  need  of  rest  for  repairing  in 
disease  ? 


14  FIRST   BOOK   IN   PHYSIOLOGY. 

it  as  much  as  is  possible  ;  that  is,  it  must  be  kept  from 
thinking.  And  what  is  true  of  particular  parts  of  the 
machinery  is  true  of  it  as  a  whole.  When  the  whole 
body  is  disordered,  as  in  fever,  all  the  machinery 
must  be  kept  as  quiet  as  possible. 

17.  There  is  some  of  the  machinery  that  never  stops, 
either  when  we  are  sick  or  when  we  are  asleep ;  it 
is  the  breathing  and  the  circulating  machinery.     The 
heart  is  always  beating,  and  the  chest  is  always  heav- 
ing ;  they  never  rest  from  their  work,  and  they  are 
stopped  only  by  death. 

18.  In  this  chapter  I  have  given  you  some  general 
views  of  the  machinery  of  the  body.     In  the  follow- 
ing chapters  I  shall  describe  particular  parts  of  it,  and 
shall  explain  to  you  how  they  operate.     I  shall  speak 
of  the  machinery  of  digestion,  of  circulation,  of  respi- 
ration, the  nervous  machinery,   &c.,  each  of  them 
separately. 


CHAPTER  II. 

THE   DIFFERENT   STRUCTURES   OF  THE   BODY. 

1.  BEFOKE  considering  each  subject  particularly, 
let  us  look  in  this  chapter  at  some  of  the  various 
things  or  structures  that  make  up  the  machinery  of 
the  body.  By  doing  this,  these  subjects  will  be  more 
clear  to  you.  For,  as  I  shall  mention  different  parts 
of  the  body,  as  I  proceed,  you  will  understand  me 
better,  if  you  have  some  knowledge  of  these  parts  at 
the  beginning. 

What  parts  of  the  machinery  of  the  body  never  rest  ? 


DIFFERENT  STRUCTURES  OF  THE  BODY.  15 


2.  Notice  first,  the  hard  bones  which  are  the  frame- 
work of  the  body.     These  are  very  different  in  their 
shapes  in  different  parts  of  the  frame.    For  example, 
in  the  leg  and  arm  they  are  long  and  slender,  while 
in  the  head  they  make  a  box  to  hold  the  brain.    They 
vary  much  in  size  also. 

3.  The  bones  are  composed  partly  of  mineral  and 
partly  of  animal  substance.     When  you  see  a  pile  of 
bones  near  a  slaughter-house,  which  have  been  a  long 
time  exposed  to  the  air,  you  see  only  the  mineral  part 
of  them.     The  animal  or  soft  part  has  been  taken 
away  by  the  heat  of  the  sun  and  the  washing  of  the 
rain.     The  same  thing  can  be  done,  very  quickly,  by 
exposing  a  bone  to  a  very  hot  fire.      A  bone  thus 
deprived  of  its  animal   part 

is  very  brittle,  and    breaks 
easily. 

4.  The   animal  part   of  a 
bone   can   be   obtained   also 
separate   from    the    mineral 
part.     This  can  be  done  by 
putting  it  into  a  mixture  of 
an  acid,  called  muriatic  acid, 
and  water.     The  acid  takes 
the  mineral  part  away,  and 
leaves  the  animal  part  in  per- 
fect shape.     While  the  mine- 
ral part  is   brittle,    this  soft 
animal  part  can  be  bent  so  as 


FIG.  l. 


What  is  said  of  the  shapes  of  the  bones,  and  of  their  size?  Of  whal 
two  parts  is  bone  composed  ?  How  can  the  mineral  part  be  obtained 
separate  from  the  other  part  ?  How  can  the  animal  part  be  obtained 
by  itself? 


16  FIRST   BOOK   IN    PHYSIOLOGY. 

to  be  tied  into  a  knot,  if  the  bone  be  one  of  the  long 
ones.  Fig.  1  represents  a  thigh-bone  thus  tied,  after 
being  deprived  of  its  mineral  part. 

5.  In  the  child,  when  the  bones  are  growing,  they 
do  not  have  as  much  of  the  mineral  part  as  the  bones 
of  old  persons  do.     It  is  well  that  they  do  not ;  for  if 
they  did,  the  frequent  falls  of  the  child  would  often 
give  him  a  broken  bone.     If  an  old  person  should 
have  as  many  falls  as  children  commonly  do,  his  brit- 
tle bones   would  very  often   snap  asunder.     A   fall 
down  stairs,  which  in  the  child  is  generally  followed 
only  by  a  momentary  fright,  a  short  crying-spell,  and 
perhaps  a  bruise,  is  apt  to  break  some  bone  in  the 
old,  and  may  even  destroy  life. 

6.  The  bones  are  bound  together  by  firm  ligaments, 
so  that  while  they  move  on  each  other  at  the  joints, 
they  are  held  in  their  places.     The  bones  are  moved 
by  muscles.     The  muscles  make  up  the  bulk  of  the 
fleshy  part  of  the  body.     Their  color  is  red.     The 
tendons  are  white  and  shining  cords,  by  which  the 
muscles  pull  the  bones,  in  moving  them. 

7.  As  I  must  refer  occasionally  to  the  action  of 
muscles  before  I  come  to  the  chapter  on  the  muscles, 
I  will  explain  to  you  now  the  manner  in  which  they 
act.     A  muscle  is  composed  of  a  great  number  of 
very  small  fibres  or  threads.     When  it  acts,  each  one 
of  these  fibres  shortens  itself. 

What  is  the  difference  between  the  bones  of  the  old  and  those  of  the 
young  in  regard  to  these  two  parts  ?  What  would  happen  to  the  child 
if  there  were  not  this  difference  ?  By  what  are  the  bones  bound 
together  ?  By  what  are  they  moved  ?  What  are  the  tendons  ?  What 
is  a  muscle  composed  of? 


a 


Fio.  2. 


FIG.  3. 


DIFFERENT   STRUCTURES   OF   THE   BODY.  17 

8.  I   will  show   how   this 
shortening  of  the  fibres  moves 
the  bones,  by  means  of  some 
figures.     Suppose  «,  in  Fig. 
2,  is  a  bone  that  is  fixed  so 
that  it  cannot  be  moved,  and 
that  5  can  be  moved.     Let  c 
be  a  fibre  that  extends  from 
the  one  bone  to  the  other.    If 
the  fibre  c  shorten  itself,  it  will 
draw  the  bone  ~b  towards  #,  as 
represented  in  the  lower  figure. 
The   same  thing    is  true   of    a 
number  of  fibres,  as  represented 
in  Fig.  3.    You  se^,  then,  how 
it  is  true  of  a  multitude  of  fibres, 
as  they  are  bound  together  in  a 
muscle. 

9.  Let  d,  in  Fig.  4,  represent  a 
bone  that  is  fixed,  and  e  a  bone 
that  moves  on  <#,  with  a  hinge-like 
joint.     If  the  fibres  are  relaxed, 
the  bone  e  will  be  as  in  Fig.  4 ; 
but  if  the  fibres  contract,  the  bone 
will  be  as  in  Fig.  5.     These  two 

figures  show  the  action  of  the  lower  jaw,  as  it  is 
moved  up  and  down  by  the  muscles,  in  eating.  In 
Fig.  4,  e  is  like  the  lower  jaw  when  it  is  down  ;  and 
in  Fig.  5  it  is  like  it  when  it  is  up,  so  that  its  teeth 
press  against  those  of  the  fixed  upper  jaw. 


FIGS.  4,  5. 

a 


rffi 


\    ilium 


Explain  by  figures  2  and  3,  how  the  fibres  of  a  muscle  act    Illus- 
trate the  manner  in  which  the  muscles  move  the  lower  jaw  in  eating. 


18  FIRST   BOOK   IN   PHYSIOLOGY. 

10.  Figs.  6  and  7  show  you 
how  the  muscle  that  bends 
the  elbow  acts.  In  Fig.  6  the 
bones  a  and  b  are  represented 
as  they  are  when  the  arm  is 
extended  out  straight.  The 
muscle  which  is  represented 
by  the  line  c,  is  relaxed. 

When  it  contracts  or  shortens  itself,  the  bone  b  will 

be  bent  upon  #,  as  seen  in  Fig.  7. 

11.  These  two  examples  of  muscular  action  will  be 
sufficient  for  the  present.     In  some  of  the  succeeding 
chapters  you  will  see   examples  of  other  ways  in 
which  the  muscles  operate ;  and,  in  the  chapter  on 
the  muscles,  the  many  various  ways  in  which  they 
act  will  be  fully  illustrated. 

12.  I  have  thus  spoken  of  the  bones  with  their  lig- 
aments, and  the   muscles  with   their  tendons.     The 
limbs  of  the  body  are  made  up  of  these  four  struc- 
tures.    They  compose  also  all  the  outer  parts  or  walls 
of  the  trunk  of  the  body  and  of  the  head.     Within 
these  walls  are  the  three  great  cavities  of  the  body, 
containing  its  most  important  organs. 

13.  In  the  cavity  of  the  head  is  the  brain.     This 
delicate  and  soft  organ  is  shut  in  very  securely  by 
that  round  box  of  bones,  called  the  cranium  or  skull. 
The  cavity  of  the  chest  contains  the  heart  and  the 
lungs.    The  walls  of  this  cavity  are  the  spinal  column, 
or  back-bone,  as  it  called,  the  ribs,  and  the  breast- 
Illustrate  the  manner  in  which  the  muscles  bend  the  arm  at  the 

elbow.     Of  what  four  structures  are  the  limbs  of  the  body  composed  ? 
What  other  parts  do  they  compose  ? 


DIFFERENT   STRUCTURES   OF  THE  BODY.  19 

bone.  -These  are  strongly  bound  together  by  muscles 
and  ligaments.  In  the  cavity  of  the  abdomen  are  the 
stomach,  liver,  &c.  Its  walls  are  the  spine  behind, 
and  at  the  sides  and  in  front,  broad  flat  muscles  and 
tendons.  The  organs  contained  in  these  three  cavi- 
ties I  shall  speak  of  in  other  parts  of  this  book. 

14:.  In  all  the  different  structures  of  the  body  of 
which  I  have  spoken,  there  are  blood-vessels,  large 
and  small,  circulating  the  blood  everywhere.  Nerves 
too  go  everywhere,  branching  out  from  the  brain  and 
spinal  marrow.  They  are  whitish  cords,  which  by 
dividing  continually  are  distributed  to  all  parts  of  the 
body.  The  blood-vessels  and  nerves  are  everywhere 
mingled  together.  For  if  you  prick  any  part,  the 
nerves  feel  the  pain,  and  the  blood-vessels  at  the  same 
time  let  out  their  blood. 

15.  All  the  parts  and  organs  of  the  body  are  well 
packed  together.     They  are  so  arranged  that  there  is 
no  loss  of  room.     And  there  is  a  kind  of  packing 
material  made  use  of  everywhere  between   all  the 
parts.     It  is  a  very  fine  and  nice  material.     You  can 
see  it  if  you  look  at  a  piece  of  meat  from  any  animal. 
If  you  pull  the  fibres  of  the  meat  a  little  apart,  you 
will  see  a  delicate  white  substance  between  them. 
You  will  also  see  different  portions  of  the  meat  sepa- 
rated from  each  other  by  considerable  layers  of  this 
substance.     These  are  the  different  muscles  with  the 
packing  material  between  them. 

16.  This  packing  material,  which  is  called  the  eel- 

What  are  the  three  great  cavities  of  the  body  ?  What  are  their 
walls  ?  What  do  they  contain  ?  What  is  said  of  blood-vessels  and 
nerves  in  the  different  structures  of  the  body  ?  What  is  said  of  the 
packing  of  the  parts  of  the  body  ? 


20  FIRST   BOOK   IN   PHYSIOLOGY. 

lular  membrane,  is  not  only  around  all  the  muscles 
and  between  their  fibres,  but  it  is  around  everything 
and  in  almost  everything  in  the  body.  It  is  full  of 
little  cells  or  spaces ;  and  hence  comes  its  name.  In 
some  parts  these  cells  are  larger  than  in  others.  The 
fat  of  the  body  is  in  cells  of  this  substance,  mostly 
just  under  the  skin.  When  the  cells  contain  fat  they 
are  larger  than  they  usually  are. 

17.  This  cellular  substance  is  very  yielding,  so  that 
the  motions  of  the  body  are  not  made  less  free  by 
their  being  thus  bound  together  by  this  packing  ma- 
terial.    When  the  muscles  are  performing  some  of 
their  motions  this  substance  is  very  much  moved  and 
stretched,  but  it  always  yields  easily  and  is  not  torn. 

18.  The  cells  of  this  substance  are  kept  moist  by 
a  very  little  watery   fluid.      When  this  fluid  is  in 
greater  quantity  than  it  should  be,  the  disease  called 
dropsy  is  present ;  and  it  is  because  the  cells  every- 
where open  into  each  other,  that  the  water  in  this 
disease  is  so  apt  to  accumulate  in  the  lowest  parts  of 
the  lower  limbs. 

19.  Over  all  the  parts  of  the  body  is  the  skin  cover- 
ing them  up  from  our  view.     It  also  defends  them 
from  injury.     While  for  this  purpose  it  is  very  firm, 
it  is  at  the  same  time  quite  yielding,  so  that  it  may 
not  restrain  the  motions  of  the  body.     Underneath 
the  skin  the  cellular  substance  is  very  abundant,  con- 
necting the  skin  with  the  muscles  and  other  parts. 

20.  There   is  a  kind  of   skin,  called   the  mucous 


Describe  the  appearance  of  the  common  packing  material.  What  is 
said  of  the  fat  ?  What  is  said  of  the  yielding  character  of  the  cellular 
membrane  ?  What  is  said  of  its  cells  ?  What  is  said  of  the  skin  ? 


DIFFERENT   STRUCTURES   OF  THE   BODY.  21 

membrane,  that  begins  in  the  mouth  and  nose,  and 
lines  all  the  passages  to  the  lungs,  the  stomach,  and 
other  organs.  It  may  be  called  the  interior  skin  of 
the  body.  It  is  termed  the  mucous  membrane,  be- 
cause it  is  moistened  by  mucus,  a  glairy  fluid  which 
constantly  oozes  from  it.  The  red  covering  of  the 
lips  does  not  seem  to  be  either  skin  or  mucous  mem- 
brane, but  a  texture  somewhat  like  both  of  them. 

21.  The  serous  membranes  are  so  called  because 
they  are  moistened  with  a  watery  fluid  called  serum. 
They  line  the  outside  of  some  of  the  great  organs  of 
the  body,  and  also  the  inside  of  the  walls  of  the  cavi- 
ties that  hold  them.     Thus  the  lungs  are  covered  with 
a  serous  membrane,  and  the  inside  of  the  walls  of  the 
chest  is  lined  with  it.     You  can  see  what  the  object 
of  this  is  :  as  the  chest  moves  in  breathing,  the  lungs 
rub  a  little  against  the  walls  of  the  chest ;  but  the 
smooth  shining  serous  membrane  that  lines  them  pre- 
vents the  rubbing  from  doing  any  harm.     The  same 
thing  is  true  of  the  organs  in  the  abdomen.     The  rub- 
bing of  the  stomach  and  the  intestines  against  each 
other  and  against  the  walls  of  the  abdomen,  would 
make  them  sore  and  inflamed,  if  they  were  not  all 
lined  with  this  smooth  and  moistened  membrane. 

22.  I  have  not  described  to  you  all  the  structures 
in  the  body,  but  only  those  that  it  is  well  for  you  to 
understand  in  the  beginning.     You  will  know  more 
in  relation  to  these  as  I  proceed,  and  I  shall  also  de- 
scribe to  you  in  the  succeeding  chapters  some  other 
structures. 

What  is  said  of  the  mucous  membrane  ?  "What  is  said  of  the  red 
skin  of  the  lips  ?  What  are  the  serous  membranes  ?  What  do  they 
line  ?  Of  what  use  are  they  in  the  chest,  and  in  the  abdomen  ? 


22  FIRST   BOOK   IN   PHYSIOLOGY. 

CHAPTER    III. 

DIGESTION. 

1.  I  HAVE  already  told  you  in  the  first  chapter  that 
the  blood,  which  is  the  common  building  material  of 
the  body,  is  made  out  of  the  food  that  we  eat.    That 
this  may  be  done,  the  food  must  be  digested,  as  it  is 
termed. 

2.  Digestion  is  not  a  single  and  simple  process; 
several  things  are  done.     First,  the  food  is  cut  and 
ground  by  a  sort  of  mill  in  the  mouth  ;  and  while  this 
is  going  on  the  food  is  thoroughly  moistened  by  a 
liquid  called  the  saliva.     As  fast  as  it  is  ground  and 
moistened  it  is  passed  through  a  tube  that  extends 
from  the  batjk  part  of  the  throat  down  into  the  stom- 
ach.    There  the  food  is  mixed  with  another  liquid 
called  the  gastric  juice.     It  is  then  passed  on  into  the 
intestines.     There  all  thaj;  part  of  the  food  that  can 
be  used  to  make  blood  is  sucked  up  by  a  multitude  of 
little  vessels.     These  vessels  join  together  to  form  a 
tube  which  empties  itself  into  the  blood.  Having  thus 
described  in  a  general  way  the  manner  in  which  the 
nourishing  part  of  our  food  is  separated  and  extracted 
from  it,  let  us  look  at  the  different  parts  of  the  pro- 
cess more  particularly. 

3.  First,  the  food    is  cut  and  ground  up  by  the 
teeth.     The  teeth,  in  order  to  be  fitted  for  this  work, 

From  what  is  the  blood  made  ?  Is  digestion  one  simple  process  ? 
What  is  jfe|£  done  to  the  food  ?  By  what  is  the  food  moistened  ? 
What  is  done  with  it  after  it  is  ground  and  moistened  ?  What  is  mixed 
with  the  food  in  the  stomach  ?  Into  what  does  it  pass  from  the  stom- 
ach ?  What  is  done  with  it  in  the  intestines  ? 


DIGESTION.  23 


are  made  very  hard.  They  are  the  hardest  sub- 
stances in  the  body.  None  of  the  bones  are  as  hard 
as  they  are.  Their  hardness  is  owing  to  the  enamel. 
This  forms  a  thick  coat  over  all  the  body  of  the  tooth 
down  to  the  gum.  It  does  not  extend  down  on  the 
roots,  for  it  is  not  wanted  there.  The  roots  and  all 
the  inner  part  of  the  teeth  are  like  common  bone. 
The  roots  are  fitted  into  sockets  in  the  jaws  so  firmly 
that,  as  every  one  knows,  it  is  very  hard  to  pull  them 
out. 

4.  In  Fig.  8  you  see  a  representation  of  half  of  the 
teeth  of  the  upper  jaw.    Notice  the  difference  in  their 


shape.  At  a  a  are  the  two  front  cutting  teeth.  They 
nave  sharp  edges.  At  d  d  d  are  the  three  large  back 
teeth.  These  have,  instead  of  cutting  edges,  broad 
irregular  surfaces,  so  that  they  can  grind  the  food  be- 
tween them  and  the  same  teeth  in  the  lower  jaw.  At 
c  c  are  two  smaller  grinders.  At  5  is  what  is  com- 
monly called  the  eye-tooth.  It  is  so  shaped  that  it 
neither  cuts  nor  grinds,  but  tears.  The  tooth  in  the 

What  is  said  of  the  teeth  ?     What  is  the  enamel,  and  how  is  it  ar- 
ranged on  the  teeth  ?    Describe  the  different  kinds  of  teeth  in  man  ? 


24 


FIRST   BOOK   IN    PHYSIOLOGY. 


FIG.  9. 


lower  jaw  that  is  like  it  is  called  the  stomach-tooth. 
You  see  then  that  man  has  three  kinds  of  teeth  for 
eating  his  different  kinds  of  food,  viz.,  cutting,  tear- 
ing and  grinding  teeth. 

5.  Different  animals  have 
different  kinds  of  teeth,  ac- 
cording to  the  kinds  of  food 
which  they  eat.  In  Fig.  9 
you  see  the  teeth  of  an  ani- 
mal that  lives  on  flesh  alone, 
called  a  carnivorous  animal. 
The  front  teeth  are  tearing 
ones,  while  the  back  teeth 
have  sharp  edges  for  cutting.  The  flesh  is  first  torn  by 
the  front  teeth,  and  then  it  is  cut  up  by  the  back  ones. 
You  can  see  these  two  kinds  of  teeth  in  the  mouth  of 
the  dog.  The  tearing  teeth  are  long.  When  the  jaws 
are  closed  the  ends  of  these  teeth  do  not  press  upon  the 
ends  of  the  teeth  that  are  opposite  to  them,  but 
the  teeth  pass  by  each  other,  as  you  see  in  Fig.  10, 


FIG.  10. 


Describe  the  teeth  of  carnivorous  animals.     What  arrangement  of 
their  tearing  teeth  gives  them  great  power  ? 


DIGESTION. 


26 


Fio.  11. 


which  is  a  representation  of  the  jaws  of  a  tiger.  You 
see  at  once  that  this  arrangement  of  these  long  tear- 
ing teeth  gives  them  great  power  in  tearing  flesh  to 
pieces. 

6.  Animals  that  live  on  vegetable  food,  called  h#r- 
frivomus  animals,  have  no  tearing  teeth.     The  horse 
and  the  cow  are  of  this  class.     They  have  two  kinds 
of  teeth.     There  are  cutting  teeth  in  front,  by  which 
they  crop  the  grass  or  draw  the  hay  from  the  rack. 
There  are  also  grinding  teeth  by  which  they  grind  up 
the  food  before  they  swallow  it.     In  Fig.  11  you  see 
the  rough  surface  of  some  of 

these  teeth.  There  is  a  pecu- 
liar arrangement  of  the  enamel, 
which  admirably  fits  them  to 
grind  up  the  fibres  of  the  grass.  The  enamel  is  net 
merely  on  the  outside  as  it  is  in  our  teeth,  but  there 
are  ridges  of  it,  as  you  see,  standing  up  in  the  middle 
of  each  tooth. 

7.  Those  animals  that  live  on  soft 
fruits  do  not  need  such  grinders  as 
the  grass-eating   animals  do.     They 
therefore  have  rounded  teeth  which 
serve  to  crush  their  food  as  repre- 
sented in  Fig.  12. 

8.  In  the  cutting,  and  tearing,  and  grinding  of  our 
food  the  lower  jaw  is  moved  against  the  upper  one 
by  means  of  muscles.     They  are  the  workmen  of  the 
mill,  as  we  may  say.     These  muscles  work  differently 


Fio.  12. 


Describe  the  teeth  of  herbivorous  animals.     What  peculiar  arrange- 
ment of  the  enamel  do  they  have  ?     What  are  the  teeth  of  animals  that 
eat  soft  fruits  ? 
2 


26  FIRST   BOOK   IN    PHYSIOLOGY. 

in  different  animals,  according  to  the  kind  of  food 
and  according  to  the  character  of  the  teeth.  Thus, 
when  an  animal  eats  vegetable  food  and  has  grinding 
teeth,  the  muscles  have  the  power  of  making  the 
grinding  motion.  If  it  wTere  not  so,  the  grinding  teeth 
could  not  grind,  but  could  only  crush.  You  can  see 
the  difference  between  the  grinding  and  tearing  motion 
of  the  jaws,  if  you  watch  a  dog  and  a  cow  while  they 
are  eating.  The  dog,  as  he  tears  his  food,  moves  his 
lower  jaw  up  and  down  against  the  upper  jaw  like  a 
hinge.  But  the  cow,  as  she  chews  her  cud,  gives  to 
her  jaw  a  side  wise  motion,  together  with  the  hinge- 
like  motion,  and  thus  grinds  the  food.  The  dog  does 
not  need  to  grind  his  food  as  the  cow  does,  and  there- 
fore he  has  no  grinding  teeth  and  no  muscles  that  can 
perform  the  grinding  motion. 

9.  Man  eats  all  kinds  of  food,  or  is  omnivorous ; 
he  therefore  has  the  various  kinds  of  teeth.     But  ob- 
serve, that  his  grinding  teeth  are  not  such  thorough 
grinders  as  the  cow  and  the  horse  have.     He  does  not 
need  the  ridges  of  enamel  to  grind  the  vegetable  food 
that  he  eats,  most  of  which  he  softens  by  cooking  it. 
Observe,  too,  that  his  tearing  teeth  are  not  so  long 
and  so  powerful  as  those  that  you  see  in  the  mouth 
of  the  dog  and  the   tiger.     The  reason  is,  that  he 
knows  how  to  invent  and  use  cutting  instruments,  and 
therefore  divides  his  food  very  much  before  he  eats 
it. 

10.  As  the  food  is  cut  and  ground  by  the  teeth,  it 

Illustrate  the  difference  in  the  working  of  the  muscles  in  the  carnivor- 
ous and  herbivorous.  Why  is  man  called  omnivorous?  Why  are  his 
grinding  teeth  less  powerful  than  they  are  in  animals? 


DIGESTION.  27 


is  well  moistened  by  the  fluid  in  the  mouth  called  the 
saliva.  This  fluid  is  made  in  some  glands  in  the 
neighborhood.  The  largest  of  these  glands,  or  saliva- 
factories,  as  we  may  call  them,  is  just  under  the  ear. 
It  is  this  gland  that  is  so  much  swelled  in  the  disease 
called  mumps.  There  are  three  pairs  of  these  glands, 
and  they  have  ducts  or  pipes  going  from  them,  which 
open  on  the  inside  of  the  mouth.  They  are  always  at 
work  making  the  saliva  to  keep  the  mouth  moist,  but 
they  are  especially  busy  while  we  are  eating,  in  order 
that  the  food  may  be  properly  moistened. 

11.  All  these  three  pairs  of  factories  do  not  make 
the  same  kind  of  fluid.     One  pair  make  a  fluid  which 
is  a  little  thicker  than  that  which  is  made  by  the  other 
two  pairs.     It  is  curious  to  see  the  reason  of  this  dif- 
ference.    The  thin  fluid  is  mixed  with  the  food  while 
the  mill  is  grinding  it.     The  thick  fluid  is  not  poured 
out  at  all  while  this  is  going  on ;  but  the  moment 
that  we  stop  chewing,  and  the  food  is  thrust  back  into 
the  throat  to  be  swallowed,  the  thick  fluid  is  poured 
out  and  covers  the  food,  so  that  it  may  slip  down 
easily  into  the  stomach. 

12.  The  tube  through  which  the  food  passes  down 
into  the  stomach  is  called  the  oesophagus,  or  gullet. 
In  Fig.  13  is  represented  the  inside  of  the  stomach  with 
the  beginning  of  the  intestines.     At  3  is  the  left  end 
and  at  4  is  the  right  end.     At  1  is  the  opening  of  the 
gullet  into  the  stomach.     At  5  is  a  valve  which  is 
sometimes  shut,  so  as  to  prevent  anything  from  pass- 
By  what  is  the  saliva  made?     Where  is  the  largest  of  these  glands 

situated  ?  How  many  of  these  glands  are  there  ?  Are  they  equally  at 
work  all  the  time  ?  Do  they  all  secrete  the  same  kind  of  fluid  ?  What 
is  the  use  of  the  thicker  fluid  made  by  one  pair  of  these  glands? 


28  FIRST   BOOK    IN   PHYSIOLOGY. 


ing  from  the  stomach  into  the  intestine.     This  valve 
is  called  the  pylorus. 

13.  While  the  food  is  in  the  stomach  the  gastric 
juice  oozes  out  from  all  the  inside  lining,  marked  8, 
and  mixes  up  with  the  food.     The  mixture  is  very 
thoroughly  made,  because  the  stomach  keeps  up  a 
sort   of  churning   motion.     After   awhile   the  food, 
although  it  is  sometimes  of  so  many  different  kinds, 
is  all  changed  into  a  greyish   cream-like  substance, 
called  chyme. 

14.  None  of  the  food  can  pass  by  the  valve  into  the 
intestines  till   the  gastric    juice   has   acted   upon  it 
enough  and  changed  it  into  chyme.     As  the  stomach 
churns  the  food,  some  of  it  continually  comes  in  con- 
tact with  the  valve.     But  the  valve  will  not  open  till 
some  of  it  comes  along  that  is  fit  to  pass.     If  the  food 

Describe  the  stomach  as  shown  in  Fig.  13.  Where  does  the  gastric 
juice  come  from  ?  How  is  it  mixed  thoroughly  with  the  food  ?  What 
is  the  chyme?  Describe  the  operation  of  the  valve  called  the  pylorus. 


DIGESTION. 


29 


is  not  digested,  as  sometimes  happens,  then  commonly 
this  sentinel  after  awhile  gives  up  its  resistance,  and 
lets  the  undigested  food  pass  on.  Or,  if  it  holds  out 
in  its  resistance,  the  food  is  got  rid  of  b j  being  thrown 
back  by  the  stomach  through  the  oesophagus  or  gullet. 
15.  When  the  chyme  passes  through  the  valve  of 
the  stomach  it  goes  into  the  intestine,  the  beginning 
of  which  you  see  in  Fig.  13.  There  two  other  juices 


Liver.    Pylorus. 


Pancreas.  Stomach. 


pleen. 

Large  Intestines, 
mall  Intestines. 


Gall  Bladder,- 


Large  Intestines. 


Beginning  of 
Large  Intestines. 

"Worm-like 

Appendage. 


Small  Intestines. 

are  poured  in  and  mingled-  with  it.     The  duct  from 
the  liver  is  represented  in  the  figure  at  6,  and  the  duct 

Into  what  does  the  chyuie  pass  from  the  stomach  ?     What  two  juices 
are  here  mingled  with  it  ? 


30 


FIRST    BOOK    IN    PHYSIOLOGY. 


from  the  pancreas  opens  near  it.  These  fluids  come 
from  two  glands.  One  of  these  glands  is  a  very  large 
one,  the  liver.  You  see  this  gland  in  Fig.  14,  which 
gives  a  general  view  of  the  digestive  organs.  The 
juice  from  this  gland  is  called  bile.  It  is  of  a  yellow 
color  and  is  very  bitter.  The  other  juice  comes  from 
a  gland  called  the  pancreas,  which  you  see  in  the 
figure,  lying  behind  the  end  of  the  stomach.  This  is 
very  mild  and  is  much  like  the  saliva  with  which  the 
food  is  moistened  while  the  teeth  are  grinding  it. 

16.  There  is  a  curious  arrangement  of  the  bile  duct 
or  duct  from  the  liver,  which  I  will  notice.  "While  it 
goes  direct  from  the  liver  to  the  intestine,  like  the 
duct  from  the  pancreas,  a  branch  goes  back  from  it 
to  the  gall-bladder,  as  it  is  called.  This  arrangement 
is  represented  in  Fig.  15,  in  which  a  is  the  intestine 
cut  open,  b  is  the  duct  which  is  made 
by  the  joining  together  of  many  little 
ducts  from  the  liver,  c  is  the  gall-blad- 
der, and  d  is  the  duct  which  goes  from 
the  gall-bladder  to  join  the  duct  from 
the  liver.  The  object  of  this  arrange- 
ment is  plain.  The  bile  is  needed  in 
the  intestine  in  considerable  quantity 
whenever  there  is  chyme  there  for  the 
bile  to  act  upon.  But  the  liver  is  a 
large  organ,  or  a  large  factory,  as  we 
may  call  it,  and  is  all  the  time  making 
bile.  The  gall-bladder  is  a  convenient  place  of  de- 
posit, or  reservoir,  where  tne  bile  is  stored  up  until  it 

From  what  glands  do  these  juices  come  ?     Describe  the  arrangement 
of  the  gall-bladder  and  the  ducts. 


DIGESTION.  31 


is  needed.  When  there  is  no  chyme  in  the  intestine, 
the  bile,  as  it  flows  from  the  liver  in  the  duct  J,  takes 
a  turn  by  the  branch  d  into  the  gall-bladder.  In  what 
way  it  is  made  to  take  this  sharp  turn  we  do  not 
know.  After  we  have  eaten  a  meal,  and  the  chyme 
begins  to  be  poured  from  the  stomach  into  the  intes- 
tine, then  much  bile  is  needed,  and  it  comes  freely 
both  from  the  liver  and  from  the  gall-bladder. 

IT.  We  do  not  know  exactly  what  the  bile  and  the 
juice  from  the  pancreas  do  to  the  chyme.  It  is  sup- 
posed that  they  separate  the  nourishing  part  of  the 
chyme  from  that  which  is  not  nourishing,  as  the  chyme 
passes  along  through  the  intestines.  As  this  chyle  (so 
called)  is  thus  separated,  it  is  sucked  up  or  absorbed 
by  vessels  scattered  all  over  the  inside  of  the  intes- 
tines. These  absorbents  are  called  lacteals,  from  lac, 
meaning  milk,  because  the  fluid  which  they  absorb 
is  a  milk-like  fluid. 

18.  The  lacteals  are  exceedingly  small,  and  cannot 
be  counted.      They  do  their  work   very  faithfully. 
They  will  commonly  take  up  nothing  but  the  chyle. 
Anything  else  that  comes  along  they  shut  their  mouths 
against  and  let  it  pass  on. 

19.  The  chyle  is  that  which  makes  all  the  blood.  It 
must  therefore  in  some  way  be  poured  into  the  circu- 
lation, and  I  will  tell  you  how  this  is  done.     The  lit- 
tle vessels  that  drink  it  up  from  the  chyme  unite  to- 
gether to  form  a  tube  about  the  size  of  a  quill.     This 
tube  runs  up  in  front  of  the  back-bone,  and  at  the  top 

What  is  the  office  of  the  gall-bladder  ?  What  effect  do  the  bile  and 
juice  from  the  pancreas  produce  upon  the  chyme?  What  is  the  chyle? 
What  are  the  lacteal*? 


32  FIRST   BX»K   IN   PHYSIOLOGY. 


of  the  chest  empties  the  chyle  into  the  blood  where 
two  large  veins  unite  together.  And  now  this  whitish 
milky  fluid  becomes  blood,  and  is  carried  every- 
where to  nourish  the  body. 

20.  In  Fig.  14  you  see  ell  the  complicated  apparatus 
or  machinery  of  digestion,  except  its  mill  or  grinding 
part  where  the  process  begins.     The  parts  are  not 
closely  packed  together  as  they  are  in  the  body,  but 
they  are  represented  as  a  little  separated  from  each 
other,  so  that  you  may  see  them  more  clearly  and 
fully.     As  this  is  a  front  view  the  left  side  of  the 
figure  is  the  right  side  of  the  parts.     The  large  encT  of 
the  stomach,  which  is  at  the  right  side  of  the  figure, 
is  on  the  left  side  in  the  body.     You  see  that  the 
great  bulk  of  the  liver  is  therefore  on  the  right  side. 
The  spleen,  which  lies  against  the  large  end  of  the 
stomach,  is  an  organ  the  use  of  which  we  do  not 
understand.     Neither  does  any  one  know  what  is  the 
use  of  the  little  worm-like  appendage  at  the  beginning 
of  the  large  intestines. 

21.  The  great  object  of  all  this  apparatus  is  to  ex- 
tract the  chyle,  the  nutritious  part  of  the  food,  and 
pour  it  into  the  blood.     It  is  in  this  way  that  blood  is 
made  out  of  our  food.     The  blood,  the  building  mate- 
rial of  the  body,  is  all  the  time  used  in  building  and 
repairing.     For  this  reason  there  must  be  a  constant 
fresh  supply  of  blood.     It  is  the  chyle  poured  into 
the  blood  by  its  little  tube  or  duct  that  gives  this  sup- 
ply.    If  this  tube  should  be  cut  off,  or  be  blocked  up, 

Describe  the  way  in  which  the  chyle  gets  into  the  blood.  What  does 
it  become?  Describe  the  arrangement  of  the  organs  of  digestion  in 
Fig.  14.  What  is  the  object  of  all  the  apparatus  of  digestion?  . 


DIGESTIO*  33 


the  blood  would  constantly  lessen,  the  body  would 
shrink  or  become  emaciated,  as  we  say,  and  death 
would  at  length  result.  The  same  thing  would  hap- 
pen if  the  stomach  stopped  digesting  the  food,  for 
then  no  chyle  would  be  formed,  and  therefore  no  new 
blood  would  be  made. 

22.  There  are  many  things  that  are  very  wonderful 
in  all  this  process  of  blood-making,  which  is  executed 
by  this  complicated  machinery  of  digestion.     It  is 
especially  wonderful  that  a  simple  milky  fluid  should 
be  separated  from,  such  a  great  variety  of  food  as  we 
eat  from  day  to  day,  and  then  that  this  whitish  fluid 
should  be  changed  into  red  blood. 

23.  The  apparatus  of  ""digestion  differs  in  different 
animals  according  to  the  kinds  of  food  that  they  eat. 
If  the  food  that  an  animal  eats  is  very  much  like  his 
body,  the  apparatus  or  machinery  is  quite  simple  ;  for 
the  food  in  this  case  does  not  need  to  be  changed 
much  to  make  his  blood.     But  if  the  food  which  an 
animal  lives  on  is  very  much  unlike  his  flesh,  the 
apparatus  of  digestion  is  very  complicated,  because 
the  food  must  be  much  changed  before  blood  can  be 
made  out  of  it. 

24:.  For  these  reasons  the  digestive  machinery  in 
such  animals  as  the  dog,  the  tiger,  and  the  lion,  is 
simple,  for  they  live  on  flesh,  which  is  of  course  very 
much  like  their  own  flesh.  But  in  such  animals  as 
the  cow  and  the  sheep,  this  machinery  is  complicated. 

In  what  ways  can  the  supply  of  chyle  to  the  blood  be  stopped  ? 
What  things  are  there  in  the  process  of  digestion  that  are  especially 
wonderful  ?  In  what  animals  is  the  machinery  of  digestion  most  simple  ? 
In  what  animals  is  it  complicated  ?  Illustrate  by  referring  to  different 

2* 


34  FIRST    BOOK    IN    PHYSIOLOGY. 

The  reason  is,  that  the  grass  which  they  eat  is  not  at 
all  like  their  flesh.  It  must  therefore  go  through  a 
great  change  to  fit  it  to  make  the  hlood  and  flesh  of 
such  animals.  And  this  cannot  he  done  without  con- 
siderable machinery.  The  flesh-eating  lion  has  a 
single  stomach,  and  the  length  of  its  intestines  is  only 
three  times  that  of  its  body.  But  the  grass-eating 
sheep  has  really  four  stomachs,  and  the  length  of  its 
intestines  is  twenty -eight  times  that  of  its  body.  Fig. 
16  represents  the  four  stomachs  of  the  sheep.  In  man 

FIG.  16. 


(Esophagus 


Intestine-n 

Pylorus.^        4th  gtomt  2d  gtom^        lgt  gtom> 

there  is  but  one  stomach,  and  the  length  of  his  intes- 
tines is  about  six  times  the  length  of  the  body. 

25.  In  birds  that  eat  grains  and  seeds  there  is  a  pe- 
culiar arrangement  of  the  digestive  machinery.  They 
have  no  teeth,  and  their  mill  for  grinding  their  food, 
instead  of  being  in  the  mouth,  is  in  the  stomach.  The 
gizzard,  which  is  the  stomach,  is  truly  a  mill  for 
crushing  the  food  to  pieces.  It  has  on  the  inside  two 

How  long  are  the  intestines  in  the  lion  ?  ILI  the  sheep  ?  In  man  ? 
How  many  stomachs  has  the  sheep? 


DIGESTION. 


35 


very  hard  surfaces,  which  are  rubbed  and  pressed 
together  by  stout  muscles.  The  grain  is  thus  broken 
up  j  ust  as  it  is  done  between  two  mill  stones.  While 
this  is  going  on  the  gastric  juice  comes  down  from 
above,  and  dissolves  and  digests  the  broken  grain. 

FIG.  17. 


This  arrangement  is  seen  in  Fig.  IT,  which  represents 

What  is  there  peculiar  in  the  digestive  machinery  of  grain-eating 
birds? 


36  FIRST   BOOK   IN    PHYSIOLOGY. 

the  stomach  of  a  turkey.  At  I  is  the  gizzard  cut 
open,  showing  the  two  hard  grinding  surfaces,  and  at 
a  above  is  the  part  from  which  oozes  the  gastric  j  uice. 
In  those  birds  that  live  on  flesh  or  fish  there  is  no  such 
grinding  machinery,  but  the  stomach  is  a  thin  bag, 
just  as  it  is  in  all  animals  that  live  on  such  food. 


CHAPTER    IV. 
CIRCULATION  OF  THE  BLOOD. 

1.  IN  the  last  chapter  you  saw  how  the  supply  of 
blood  is  kept  up  in  the  body.     In  this  chapter  I  shall 
show  you  how  the  blood  is  circulated  everywhere,  in 
order  that  it  may  be  used  in  building  and  repairing. 
The  machinery  that  thus  circulates  the  blood  is  called 
the  circulating  system.      It  has  its  pipes  everywhere. 
There  is  no  part  of  the  body  where  the  blood  does  not 
go.     And  this  machinery  keeps  the  blood  everywhere 
in  motion.     It  nowhere  rests  for  a  single  moment. 

2.  This  circulating  machinery  has  a  great  central 
organ,  the  heart,  situated  in  the  chest.     This  forces 
the  blood  out  all  over  the  body  through  the  arteries. 
It  receives  it  back  again  by  the  veins.     It  forces  the 
blood  out  through  a  large  artery,  called  the  aorta,  and 
from  this  go  branches   in   every  direction.      These 

Describe  the  arrangement  of  the  digestive  organs  in  the  turkey. 
"What  kind  of  stomach  have  birds  that  eat  flesh  or  fish?  What  is  the 
machinery  that  circulates  the  blood  called  ?  Is  the  blood  ever  still  any- 
where ?  What  are  the  different  parts  of  the  machinery?  Through 
what  does  the  heart  send  out  the  blood  ?  Through  what  does  it  receive 
it  back? 


CIRCULATION    OF   THE   BLOOD.  37 

branches  divide  more  and  more,  just  like  the  branches 
of  a  tree,  till  the  extreme  branches  are  exceedingly 
small. 

3.  These  small  arteries  end  in  a  network  of  vessels 
that  are  so  small  that  they  are  called  capillaries,  from 
the  Latin  word  capilla,  hair.     They  are  really  smaller 
than  any  hair.     When  you  prick  or  cut  your  finger 
you  wound  a  large  number  of  these  capillaries,  and 
they  let  out  their  blood. 

4.  The  heart  acts  like  a  forcing  and  suction  pump. 
It  pumps  out  the  blood  through  the  arteries,  and  by 
suction  it  draws  the  blood  back  by  the  veins.     It 
forces  out  the  blood  by  contracting  itself,  or  making 
itself  smaller.     It   draws  in   the  blood   by   dilating 
itself,  or  making  itself  larger. 

5.  I  will  make  these  two  actions  of  the  heart  plain 
to  you  by  certain  comparisons.     When  you  press  the 
two  sides  of  a  pair  of  bellows  together  by  the  handles, 
as  represented  in  Fig.  18,  you  contract  the  bellows — 

FIG.  18. 


that  is,  you  make  the  room  in  it  smaller.     A  part  of 

"What  are  the  capillaries?  Like  what  does  the  heart  act?  How 
does  it  force  out  the  blood  ?  And  how  does  it  draw  it  in  ?  Illustrate 
by  comparison  with  a  pair  of  bellows. 


38  FIRST   BOOK   IN    PHYSIOLOGY. 

the  air  is  therefore  forced  out  through  the  nose  of  the 
bellows.  It  is  in  the  same  way  that  the  blood  is 
forced  out  of  the  heart  through  the  aorta.  The  only 
difference  is  that  the  heart  contracts  itself,  instead  of 
having  it  done,  as  in  the  case  of  the  bellows,  by  hands 
and  handles.  Again,  when  you  move  the  handles  of 
the  bellows  apart,  as  represented  in  Fig.  19,  you 

FIG.  19. 


enlarge  the  room  in  the  bellows,  and  so  the  air  rushes 
in  to  fill  the  vacant  space.  In  like  manner,  when  the 
heart  dilates,  or  enlarges  itself,  there  is  more  room  in 
it,  and  the  blood  rushes  in  to  fill  it  up. 

6.  Another  comparison,  to  illustrate  the  contraction 
and  dilatation  of  the  heart,  is  this.  Fasten  a  tube  to 
the  neck  of  an  india-  rubber  bottle,  and  fill  it  up 
with  water.  Put  the  end  of  the  tube  in  a  vessel  of 

Illustrate  the  action  of  the  heart  by  the  comparison  of  the  india- 
rubber  bottle. 


CIRCULATION   OF   THE   BLOOD.  39 

water.  If  now  you  press  the  sides  of  the  ball  together, 
some  of  the  water  in  it  is  forced  out  into  the  vessel, 
just  as  blood  is  forced  out  through  the  aorta,  when 
the  heart  contracts.  If  now  you  stop  pressing  the 
ball,  and  let  it  take  its  round  shape  again,  the  water 
rushes  into  it  from  the  vessel.  For  the  same  reason, 
when  the  heart  dilates  or  becomes  larger,  the  blood 
rushes  into  it. 

7.  I  will  now  explain  to  you  the  manner  in  which 
the  heart  contracts  and  dilates.  The  heart  is  made 
up  of  muscular  fibres,  which  have  the  power  of  short- 
ening themselves,  as  you  saw  in  chapter  second,  §7  and 
§  8.  Now  suppose  one  of  these  fibres,  as  seen  at  #,  in 
Fig.  20,  shortens  itself  so  as  to  be  like  5,  the  space  that 

FIG.  20. 

G 


is  inclosed  in  it  becomes  smaller,  just  as  in  the  case 
of  the  bellows.  In  G  and  d  you  see  the  same  thing 
represented  when  several  fibres  are  together.  If  the 
fibres  in  c  become  shorter,  so  as  to  be  as  in  c?,  the 
space  they  inclose  is  smaller.  You  readily  see  from 
this,  that  when  all  the  fibres  of  the  heart  are  short- 
ened, the  space^in  it  is  lessened,  and  a  part  of  the 
blood  is  forced  out. 

8.  You  can  see  by  the  same  figures  how  the  heart 

Explain  by  the  Figures  the  action  of  the  muscular  fibres  of  the  heart 
when  it  contracts  and  dilates. 


40  FIRST   BOOK  IN   PHYSIOLOGY. 

dilates  or  enlarges  itself.  If  the  contracted  or  short- 
ened fibre  b  lengthens  so  as  to  be  as  0,  the  space  en- 
closed by  it  becomes  larger.  And  so  also  of  any 
number  of  fibres.  It  is  supposed  that  the  enlarged  or 
dilated  state  of  the  heart  is  its  natural  state  of  rest, 
when  the  fibres  are  not  acting,  but  are  quiet.  That 
is,  the  heart  is  really  at  work  only  when  it  contracts. 
When  it  dilates  it  merely  ceases  to  act,  and  lets  itself 
go  back  to  its  natural  size  by  its  own  elasticity,  as  it 
is  termed.  It  is  just  as  the  india-rubber  ball  goes 
back  to  its  natural  roundness  when  you  stop  press- 
ing it. 

9.  The  fibres  of  the  heart  are  not  arranged  in  the 
regular  form  in  which  they  are  represented  in  the 
above  figures.     They  meet  each  other,  and  cross  each 
other  in  various  ways.    But  the  effect  of  their  contrac- 
tion is  as  described.    You  can  see, 
for  example,  by  figure  21,  that  it 
will  make  no   difference   in   the 
effect,  whether  a  single  fibre  go 
all  around,  as  in  a,  or  whether 
two  fibres  lap  on  to  each  other,  as 

in  5,  and  are  fastened  together.  And  the  same  can 
be  said  of  any  number  of  fibres. 

10.  When   the   heart   beats,    these   fibres   shorten 
themselves,  and  the  blood  is  forced  out  into  the  arte- 
ries.    Then,  as  the  fibres  relax,  the  blood  comes  into 
the  heart  from  the  veins.     And  so  the  heart  by  turns 
con  tracts  and  enlarges,  just  as  you  contract  and  enlarge 
the  bellows  in  working  them,  as  you  blow  the  fire. 

Is  the  heart  in  action,  or  is  it  at  rest,  "when  it  dilates  ?  How  are  the 
fibres  of  the  heart  arranged?  Give  the  comparison  made  in  §10  be- 
tween the  action  of  these  fibres  and  the  action  of  the  bellows. 


CIRCULATION   OF  THE   BLOOD.  41 

11.  Let  us  look  now  at  some  things  in  which  the 
arteries  and  veins  differ  from  each  other.     You  see 
veins  lying  just  under  the  skin  in  various  parts  of  the 
body,  but  you  do  not  see  the  arteries.     They  all  lie 
deeper  than  these  veins  that  you  see.     The  reason  is 
this.     It  would  be  dangerous  to  have  the  arteries  so 
near  the  skin  as  some  of  the  veins  are.    For  the  heart 
is  pumping  the  blood  directly  into  them  with  great 
force.     And  therefore  if  an  artery  is  cut,  it  bleeds 
much  more  than  a  vein  of  the  same  size,  and  its  bleed- 
ing is  not  as  easily  stopped.     For  this  reason   the 
Maker  of  our  bodies  has,  as  we  may  say,  laid  the 
arteries  deep,  so  that  they  cannot  often  be  cut  in  the 
accidents  that  happen  to  us. 

12.  You  can  see  that  special  pains  are  taken  in 
some  cases  to  guard  the  arteries.     Thus  the  large 
artery  of  the  arm,  when  it  comes  to  the  joint  at  the 
elbow,  does  not  pass  over  the  bones,  where  it  would 
be  apt  to  get  wounded.     It  lies  deep  on  the  inside  of 
the  elbow,  under  the  stout  tendon  that  you  feel  there. 
So  at  the  knee,  the  artery  is  deep  in  the  ham  at  the 
back  of  the  joint,  in  a  space  between  two  jutting  par- 
apets of  bone,  as  we  may  call  them. 

13.  There  are  only  a  few  places  in  the  body  where 
arteries  of  any  size  are  very  near  the  surface.  In  such 
cases  it  is  because  they  could  not  possibly  be  laid  in 
any  better  way.     One  of  these  is  the  wrist,  where  the 
physician  commonly  feels  the  pulse.     Another  is  on 
the  temples.     In  some  persons  who  are  very  thin  you 

How  do  the  arteries  and  the  veins  differ  from  each  other  in  their 
situation?  What  is  the  reason  of  this  difference?  Mention  some 
cases  in  which  special  pains  are  taken  to  guard  the  arteries. 


42  FIRST   BOOK    IN    PHYSIOLOGY. 

can  see  the  artery  on  the  temples  beating,  and  can 
count  the  pulse  there  without  being  obliged  to  feel  it. 

14.  As  the  heart  pumps  the  blood  into  the  arteries 
with  so  much  force,  they  are  made  much  stronger  than 
the  veins  are.     If  they  were  not,  they  would  often 
burst,  as  you  have  seen  the  hose  of  a  fire  engine  do. 
But  the  arteries  are  made  so  strong  that  this  is  a  very 
uncommon  accident. 

15.  What  is  called  the  pulse  I  will  explain  to  you. 
When  the  heart  contracts  it  gives  a  sudden  motion  or 
impulse  to  all  the  blood  in  all  the  firm  arteries.     The 
blood  all  moves  at  once.     The  motion  is  not  like  a 
wave,  going  from  the  heart  in  all  directions.     The 
blood  at  a  distance  from  the  heart  is  moved  at  the 
same  time  with  the  blood  near  the  heart.     It  is  this 
motion  or  impulse  that  you  feel  when  you  put  your 
finger  upon  an  artery.    The  impulse  thus  felt  is  called 
the  pulse.     You  can  feel  the  pulse  wherever  you  can 
feel  an  artery.     It  is  everywhere.     In  a  young  infant 
you  can  both  feel  and  see  the  pulse  in  the  open  space 
on  top  of  its  head,  where  the  bones  are  not  joined 
together.      This  is  the  pulse  of  the  arteries  of  the 
brain.     When  the  heart  beats  very  strongly,   as  it 
does  in  a  high  fever,  this  pulse  in  the  brain  is  very 
manifest. 

16.  If  a  vein  be  cut,  the  stream  from  it  is  a  steady 
one,  because  the  blood  flows  in  the  veins  back  to  the 
heart  slowly  and  steadily.     But  if  an  artery  be  cut, 
the  stream  is  not  steady  but  spouts  out  by  jerks  or 

In  what  places  in  the  body  are  the  arteries  very  near  the  surface, 
and  why  ?  How  do  the  arteries  and  veins  differ  in  strength,  and  why  ? 
Explain  what  the  pulse  is.  Where  can  you  feel  the  pulse  ? 


CIRCULATION   OF  THE  BLOOD.  43 

jets.  This  is  owing  to  the  impulse  that  is  given  to 
the  blood  in  the  arteries  when  the  heart  beats  or  con- 
tracts. There  is  a  jet  for  every  contraction. 

17.  It  is  well  for  every  one  to  know  how  to  stop 
the  bleeding  of  an  artery  when  it  is  wounded.  It  does 
no  good  to  wind  cloths  around,  as  is  very  commonly 
done.     This  only  catches  the  blood,  while  the  artery 
is  left  to  go  on  to  bleed.     If  you  bear  in  mind  that 
the  blood  comes  from  the  heart  in  the  artery,  you  will 
see  that  pressing  on  the  artery  on  the  side  of  the 
wound  which  is  towards  the  heart  will  stop  the  bleed- 
ing.    Firm  pressure  with  the  thumb  will  do  it  if  you 
put  the  thumb  in  the  right  place.     In  order  to  find 
the  right  place  uncover  the  wound  and  press  your 
thumb  here  and  there  till  you  see  that  the  blood  stops 
flowing  from  the  wound.    If  you  find  that  by  pressing 
in  any  spot  the  blood  is  stopped,  hold  your  thumb 
there  till  the  surgeon  comes  to  take  care  of  the  case. 
If  you  cannot  find  the  right  spot,  tie  a  slip  of  cloth  or 
a  handkerchief  around  the  limb  above  the  wound, 
and  then  twist  a  stick  in  it  till  the  bleeding  stops.     A 
child  with  this  information  may  be  able  to  save  a  life, 
and  yet  for  want  of  it  many  a  person  has  died  in  such 
a  case,  for  few  even  among  adults  understand  the 
matter. 

18.  The  object  of  the  machinery  of  the  circulation 
is  to  get  the  blood  into  the  network  of  the  capillaries, 
and  then  bring  it  back  to  the  heart.     It  is  when  the 
blood  is  in  these  capillaries  that  it  is  used  for  building 

How  does  the  stream  of  blood  from  a  cut  vein  differ  from  the  stream 
from  a  cut  artery  ?  What  is  the  reason  of  the  difference  ?  How  would 
you  etop  the  bleeding  of  an  artery  I 


44  FIRST   BOOK   IN   PHYSIOLOGY. 

and  repairing.  It  is  by  the  arteries,  as  you  have  seen, 
that  the  blood  is  brought  to  the  capillaries,  and  it  is 
by  the  veins  that  it  is  carried  back  from  them  to  the 
heart. 

19.  As  the  blood  comes  from  the  heart  by  the  arte- 
ries it  has  a  bright  red  color.     But  when  it  passes 
from  the  capillaries  into  the  veins  it  has  a  dark  color. 
The  cause  of  this  change  is  the  use  which  is  made  of 
the  blood  while  it  is  in  the  capillaries.     Something 
has  been  taken  from  it  for  building  and  repairing,  and 
so  it  cannot  be  as  good  building  material  as  it  was 
before  it  was  used.     Not  only  has  there  something 
been  taken  from  it,  but  there  has  also  been  added  to 
it  some  of  the  waste  matter  that  comes  from  the  wear 
and  tear  of  the  system.     On  becoming  dark  blood, 
then,  it  has  been  changed  from  good  blood  to  bad  blood. 

20.  This  dark  blood,  then,  that  goes  back  by  the 
veins  to  the  heart  is  not  fit  to  be  used  so  long  as  it 
remains  dark.     When  it  gets  back  to  the  heart  it  will 
not  do  to  have  it  sent  all  over  the  body  by  the  arte- 
ries.    It  would  destroy  life  everywhere.     The  organs 
of  all  the  machinery  of  the  body  would  stop  their 
operations.     For  example,  if  this  dark  blood  should 
be  sent  to  the  brain,  the  individual  would  become  in- 
sensible and  fall  down,  and  he  would  die  very  soon  if 
the  good  red  blood  could  not  be  sent  to  his  brain. 
And  so,  too,  would  all  the  organs  stop  work,  as  we  may 
say,  if  dark  blood  instead  of  red  were  sent  to  them. 

What  is  done  with  the  blood  in  the  capillaries  ?  What  is  the  color 
of  the  blood  in  the  artei-ies  ?  What  in  the  veins  ?  What  is  the  cause 
of  the  change  ?  What  is  done  to  the  blood  in  the  capillaries  ?  What 
would  happen  if  the  dark  blood  should  be  sent  to  the  organs  of  the 
body  instead  of  red  blood  ? 


CIRCULATION    OF   THE    BLOOD. 


45 


21.  This  dark  blood  then,  when  it  comes  back  to 
the  heart,  must  in  some  way  be  changed  to  red  blood 
before  the  heart  sends  it  again  all  over  the  system. 
For  this  purpose  the  heart  sends  it  to  the  lungs,  where, 
by  exposure  to  the  air  that  we  breathe  into  those 
organs,  it  is  changed  to  red  blood.     After  it  is  thus 
changed  it  comes  back  to  the  heart,  and  is  then  sent 
all  over  the  body. 

22.  All  this  could  not  be  done  by  the  heart  if  it 
were  a  single  organ.     It  is  not  single.     It  is  double,  or 
rather,  there  are  really  two  hearts ;  one  for  the  circu- 
lation all  over  the  body,  and  the  other  for  the  circu- 
lation  through  the  lungs.     The   two  hearts  are  so 
closely  united  together  that  they  are  spoken  of  as  one 
heart.     But  they  are  entirely  separate,  so  far  as  any 
communication  between   them  is  concerned.     None 
of  the  blood  in  one  can  mingle  with  that  in  the  other. 
The  blood  in  them  is  different.     In  one  heart  it  is 
red,  and  in  the  other  it  is  dark.    I  shall  speak  of  them 
as   the   two  sides   of   the  heart,  the  right  and  the 
left  side,  as  is  common- 
ly done. 

23.  That  you   may 
understand  the  course 
of  the  blood  in  the  two 
circulations,  I  shall  de- 
scribe it  by  Figure  22. 
Let    a    represent    the 
right  side  of  the  heart, 
c  the  left  side,   J  the 


FIG.  22. 


What  is  done  with  the  dark  blood  ?  Why  is  the  heart  double  ?  Are 
the  two  sides  of  the  heart  as  separate  as  if  they  were  two  hearts  ?  Is 
the  blood  of  the  same  color  in  the  two  sides  ? 


46  FIRST   BOOK    IN    PHYSIOLOGY. 

lungs,  and  d  the  general  system  of  the  body. 
The  arrows  point  in  the  direction  in  which  the  blood 
flows.  In  all  the  shaded  part  the  blood  is  dark,  and 
in  the  part  that  is  not  shaded  it  is  red.  Let  us  now 
begin  at  some  point,  and  trace  the  course  of  the 
blood.  "VYe  will  start  at  &,  the  right  side  of  the  heart. 
The  blood  received  here  from  the  whole  body  by  the 
veins  is  of  a  dark  color.  It  is  sent  by  this  right  side 
of  the  heart  to  the  lungs,  ~b.  Here  it  is  changed  to 
red  blood,  and  then  passes  back  by  veins  to  the  heart 
— but  observe,  it  is  to  the  left  side,  c.  It  is  now  sent 
by  this  left  side  of  the  heart  to  the  whole  system,  d. 
Here,  in  the  capillaries,  it  is  changed  to  dark  blood, 
and  goes  back  by  veins  to  the  right  side  of  the  heart, 
0,  where  we  started.  The  blood  is  constantly  going 
the  rounds  of  these  two  circulations,  day  and  night,  as 
long  as  life  lasts. 

24:.  The  blood  in  the  right  side  of  the  heart,  or  the 
heart  for  the  lungs,  is  dark.  The  blood  in  the  left 
side  of  the  heart,  or  the  heart  for  the  whole  body,  is 
red.  So  also  in  the  arteries  that  go  out  from  the  right 
side  of  the  heart  the  blood  is  dark,  while  that  which 
goes  out  in  the  arteries  from  the  left  side  is  red.  And 
while  dark  blood  is  brought  in  the  veins  to  the  right 
side  of  the  heart  from  the  whole  body,  the  veins  that 
come  to  the  left  side  from  the  lungs  contain  red  blood. 
That  is,  in  the  circulation  for  the  lungs  the  dark 
blood  is  in  arteries  and  the  red  in  veins,  but  in  the 
circulation  over  the  whole  system  it  is  just  the 


Describe  the  course  of  the  circulation  as  represented  in  Fig.  22.  In 
•which  side  of  the  heart  is  the  blood  red,  and  in  which  dark  ?  How  is  it 
in  the  arteries  and  veins  of  the  two  circulations  ? 


CIRCULATION   OF   THE   BLOOD. 


47 


reverse — the  dark  blood  is  in  veins  and  the  red  is  in 
arteries. 

25.  The  heart  is  not  only  two  separate  hearts,  but 
each  of  these  has  two  apartments  in  it.  One  of  these 
apartments  is  larger  than  the  other.  The  smaller 
apartment  is  called  the  auricle  and  the  larger  the 
ventricle.  This  arrangement  is  represented  in  Fig.  23. 

Fm.  23. 


The  middle  part  of  the  figure  represents  the  heart 
with  its  two  sides,  that  have  no  communication  with 
each  other ;  a  being  the  right  auricle,  ~b  the  right  ven- 
tricle, d  the  left  auricle,  and  e  the  left  ventricle.  The 
blood  is  received  in  the  right  auricle,  #,  from  the 
general  system,  f.  It  then  passes  into  the  right  ven- 
tricle, J,  and  is  forced  by  the  contraction  of  it  through 
arteries  to  the  lungs,  c.  From  the  lungs  it  comes  back 
to  the  heart,  to  the  left  side,  and  enters  the  left  auri- 
cle, d.  From  this  it  passes  into  the  left  ventricle,  e, 
from  which  it  is  sent  all  over  the  body,  repre- 
sented by/. 

Describe  the  apartments  of  the  heart.     Describe  the  circulation  as  it 
takes  place  through  these  apartments. 


48  FIRST   BOOK   IN   PHYSIOLOGY. 

26.  In  each  half  or  side  of  the  heart  the  ventricle 
is  the  main  apartment.     It  is  much  larger  than  the 
auricle.     The  auricle  is  a  sort  of  entrance-chamber 
to   the   main   apartment,   the  ventricle.     There   are 
valves,  or  folding  doors,  as  we  may  call  them,  between 
these  two  apartments.    These  valves  are  so  arranged, 
that  the   blood  can  pass  only  one   way.     Take,   for 
example,  the  valves  between  the  right  auricle,  a,  and 
the  right  ventricle,  ~b.     The  blood  can  go  from  a  to  5, 
but  it  cannot  go  from  5  to  a. 

27.  I  will  describe  to  you  the  manner  in  which  the 
blood  is  made  to  go  through  these  two  apartments. 
When  the  auricle  a  dilates  or  enlarges,  it  draws  in 
the  blood  from  the  veins  of  the  body.     It  then  con- 
tracts and  forces  the  blood  into  the  ventricle  Z>.     The 
ventricle  now  contracts,  and  sends  the  blood  towards 
the  lungs,  c.     Now,  when  the  ventricle  ~b  contracts,  it 
would  force  the  blood  back  into  the  auricle  #,  as  well 
as  forward  towards  the  lungs,  were  it  not  for  the 
valves.     When  the  ventricle  contracts  these  valves 
shut,  and  so  none  of  the  blood  can  go  in  that  direc- 
tion, but  all  of  it  goes  towards  the  lungs. 

28.  These  valves  operate  just  as  the  valve  of  the  bel- 
lows does,  as  seen  in  Figures  18  and  19,  pp.  37  and  38. 
In  Fig.  19  the  hands  are  drawing  the  handles  apart, 
and  enlarging  the  space  in  the  bellows.     Here  the 
valve  is  open  and  the  air  is  rushing  in,  just  as  the 
valves  of  the  ventricle  open  and  the  blood  rushes  in 
when  the  ventricle  dilates  or  enlarges.     In  Fig.  18 

How  are  the  valves  between  these  apartments  arranged  ?  Describe 
the  action  of  the  auricles  and  ventricles.  Compare  the  operation  of  the 
valves  between  them  to  that  of  the  valve  of  the  bellows  as  represented 
in  Figs.  18  and  19. 


CIRCULATION   OF   THE   BLOOD.  49 

the  hands  are  pressing  the  handles  together,  and  the 
valve  is  shut,  and  the  air  is  forced  out  through  the 
nose ;  just  as,  when  the  ventricle  contracts,  the  valves 
close,  and  the  blood  is  forced  out  through  the  artery 
that  goes  from  the  ventricle.  Observe  now,  in  what 
way  the  valves  are  shut  in  both  cases.  In  the  case 
of  the  bellows,  when  the  handles  are  pressed  together, 
the  air  escapes  wherever  it  can.  If  the  bellows  are 
tight,  it  escapes  only  through  the  nose.  If  the  valve 
does  not  fit  well  some  of  it  escapes  there.  The  air, 
pressing  in  all  directions,  shuts  down  the  valve,  and  if 
the  valve  is  tight  no  air  can  get  out  there.  Now,  the 
blood  does  in  the  ventricle  of  the  heart  just  as  the  air 
does  in  the  bellows.  When  the  ventricle  contracts, ' 
the  blood,  in  escaping  from  the  pressure,  shuts  the 
valves.  If  the  valves  fit  well,  as  they  commonly  do, 
none  of  the  blood  can  go  back  into  the  auricle,  but  it 
will  all  go  out  through  the  artery,  just  as  all  the  air 
goes  out  through  the  nose  of  the  bellows,  when  the 
bellows  are  tight.  There  are  other  valves  in  the 
heart,  which,  with  those  that  I  have  spoken  of,  are 
fully  described  in  my  larger  work  on  Physiology. 

29.  Having  thus  described  to  you  the  manner  in 
which  the  blood  circulates,  I  now  show  you  in  Fig.  24 
a  representation  of  the  heart  as  it  really  appears.  It 
is  a  front  view.  At  a  is  the  right  auricle.  This  re- 
ceives the  blood  from  all  parts  of  the  body  by  two 
large  veins  h  and  i,  h  bringing  the  blood  from  above, 
and  i  from  below.  At  5  is  the  right  ventricle,  which 
receives  the  blood  from  the  auricle,  and  sends  it  to 

What  shuts  the  valve  in  the  bellows  ?  What  shuts  the  valveg  in  the 
heart? 

3 


f>0  FIRST   BOOK    IN    PHYSIOLOGY 


Fio.  24. 


the  lungs  by  the  pulmonary  artery  f.  At  c  is  the  left 
auricle,  which  receives  the  blood  from  the  lungs  by 
the  pulmonary  veins  <7,  g,  g.  At  d  is  the  left  ventri- 
cle. This  receives  the  blood  from  the  auricle,  and 
forces  it  out  all  over  the  body  through  the  aorta  e. 
The  aorta,  .as  you  see,  sends  off  branches  upward  to 
the  head  and  arms,  and  then  bends  downward  behind 
the  heart  to  send  off  branches  to  all  the  other  parts  of 
the  body. 

30.  You  observe  much  irregularity  in  the  arrange- 
ment of  the  two  sides  of  the  heart,  as  they  are  called. 

Describe  the  heart  as  it  really  appears,  by  Fig.  24. 


CIRCULATION    OF   THE   BLOOD.  51 

The  auricle  a  and  the  ventricle  &  make  the  right  side. 
The  auricle  c  and  the  ventricle  d  make  the  left  side. 
In  this  front  view  of  the  heart  you  see  only  a  part  of 
the  left  side.  Much  of  the  left  auricle  and  the  left 
ventricle  are  hidden  behind  the  right  ventricle.  The 
aorta,  e,  the  large  artery  through  which  the  blood  is 
pumped  out  by  the  left  ventricle,  is  at  first  also  behind 
the  right  ventricle. 

31.  The  heart,  with  its  four  apartments  and  its  four 
sets  of  valves,  is  a  very  complicated  machine.     Yet 
commonly  it  works  well  and  easily.     One  part  does 
not  interfere  with  another.     All  the  parts  do  not  work 
at  the  same  time,  and  there  is  a  time  for  each  part  to 
act.     In  this  way  the  whole  machine  works  harmoni- 
ously. 

32.  The  two  auricles  act  together,  and  the  two  ven- 
tricles act  together  also.     For  example,  the  two  ven- 
tricles contract  together,  the  right  ventricle  pumping 
the  dark  blood  into  the  great  artery  of  the  lungs  at 
the  same  time  that  the  left  ventricle  pumps  the  red 
blood  into  the  aorta,  the  large  artery  of  the  body. 

33.  The  heart,  as  it  works  its  four  parts,  the  auri- 
cles and  the  ventricles,  makes  two  sounds.     These  you 
can  hear  if  you  put  your  ear  to  any  one's  chest  on  the 
left  side  at  its  lower  part  in  front.     You  hear  them 
better  here  than  at  any  other  spot,  because  the  heart 
here  comes  so  near  to  the  walls  of  the  chest.      You 
hear  a  heavy  and  full  sound,  followed  by  a  quicker 

What  is  said  of  the  irregularity  in  the  arrangement  of  the  parts  of 
the  heart  ?  What  is  said  of  the  complicated  character  of  the  heart, 
and  of  its  harmony  in  action  ?  What  parts  act  together  ?  Where  can 
you  best  hear  the  sounds  of  the  heart?  Why?  Describe  its  two 
sounds. 


52  FIRST   BOOK   IN   PHYSIOLOGY. 

and  lighter  one.     The  syllables  lub-tup  are  a  good 
representation  of  these  sounds. 

34.  The  heart  is  almost  wholly  covered  up  by  the 
lungs.  It  is  encased  in  a  sack  or  bag,  and  around  this 
there  is  considerable  of  the  common  packing  material 
of  the  body,  the  cellular  membrane,  spoken  of  in  the 
second  chapter.  In  Fig.  25  you  see  the  heart  between 


e          f  g   h 

the  two  lungs.  The  lungs  are  represented  as  drawn 
apart,  so  that  you  may  have  a  full  view  of  the  heart 
with  its  arteries  and  veins.  The  sac  of  the  heart  and 
the  packing  material  are  also  removed.  At  a  is  the 
trachea  or  windpipe ;  on  each  side  are  the  two  arteries 
that  go  to  the  head ;  c  is  the  artery  that  goes  to  the  arm  ; 
1)  *b  are  the  veins  coming  from  the  head,  and  d  d  the 

With  what  is  the  heart  covered  ?    Describe  its  situation  as  represent- 
ed in  Fig.  25, 


CIRCULATION   OF  THE   BLOOD.  53 

veins  from  the  arms,  all  emptying,  as  you  see,  into  a 
large  vein  that  goes  to  the  right  auricle  of  the  heart,  e ; 
f  is  the  large  vein  that  brings  the  blood  from  below 
to  this  auricle  ;  g  is  the  right  ventricle,  i  the  left,  and 
h  is  the  aorta  as  it  goes  down  from  the  heart. 

35.  The  heart  is  commonly  about  the  size  of  the 
closed  hand  of  the  individual.     It  is  a  very  powerful 
organ  for  so  small  a  one.     It  is  composed  of  mus- 
cular fibres,  and  these  are  so  nicely  arranged  that 
each  fibre  contracts  exactly  as  it  should  to  do  its  part 
of  the  work. 

36.  The  amount  of  work  that  the  heart  does  in  a 
lifetime  is  very  great.     In  an  adult  it  beats  about 
seventy  times  in  a  minute.     This  is  over  one  hundred 
thousand  times  in  twenty-four  hours.     In  the  child  it 
beats  much  faster  than  this.     And  it  is  to  be  remem- 
bered that  every  time  the  heart  beats  each  of  its  four 
parts  contracts  and  dilates.     Each  beat  of  this  organ 
is  therefore  a  complicated  movement  of  a  very  com- 
plicated machine.     And  this  machine  is  always  at 
work  as  long  as  life  lasts,  alike  while  we  are  awake 
and  while  we  are  asleep,  keeping  the  blood  in  motion 
in  all  parts  of  the  body. 

What  is  the  size  of  the  heart  ?  Of  what  is  it  composed  ?  About 
how  many  times  does  the  heart  beat  in  a  minute  ?  How  many  times 
in  twenty-four  hours  ?  How  is  it  in  children  ?  What  is  done  in  the 
heart  in  every  beat  ?  Does  the  heart  ever  rest  from  its  work  ? 


64  FIRST   BOOK    IN    PHYSIOLOGY. 

CHAPTER   V. 

RESPIRATION. 

1.  You  saw  in  the  last  chapter  that  the  dark  blood 
is  sent  to  the  lungs  by  the  heart  in  order  to  be  changed 
into  red  blood.     The  great  object  of  the  machinery 
of  the  respiration  is  to  bring  the  air  and  the  blood  to- 
gether, so  that  the  air  may  produce  this  change.  The 
way  in  which  this  machinery  operates  in  doing  this  I 
will  explain  to  you  in  this  chapter. 

2.  The  lungs  fill  up  a  large  part  of  the  chest.  They 
are  on  each  side  of  the  heart,  as  you  have  seen  in  Fig. 
25.  They  are  in  common  language  termed  the  lights; 
and  you  can  see  what  they  are  in  man  by  looking  at 
the  lights  of  other  animals.     They  are  spongy  bodies. 
They  are  full  of  very  small  air-cells.     These  give  to 
them  their  spongy  lightness  ;  and  as  a  sponge  is  much 
larger  when  its  cells  are  filled  with  water  than  when 
it  is  dry,  so  the  lungs  swell  out  when  their  cells  are 
filled  with  air.      This  can  be  shown  to  you  with  the 
lungs  of  some  animal,  as  a  sheep  or  a  calf.     If  a  tube 
be  fastened  to  the  windpipe,  you  can  make  the  lungs 
swell  out  very  much  by  blowing  air  into  them. 

3.  It  is  in  these  air-cells  that  the  air  changes  the 
dark  blood  to  red.     But  this  is  not  done  by  mixing 
up  the  blood  with  the  air  in  these  cells.     The  blood 
is  never  mixed  with  the  air  except  when  in  disease 

What  is  the  object  of  respiration  ?  What  is  the  situation  of  the 
lungs  ?  What  is  the  cause  of  their  lightness  ?  Mention  the  comparison 
between  the  lungs  and  a  sponge.  Is  the  blood  mixed  with  the  air  in  the 
lungs? 


RESPIRATION.  55 


blood  is  raised  from  the  lungs.  In  such  a  case  the 
blood  gets  into  the  air-cells  and  air-tubes.  But  in 
health  this  never  happens.  The  thin  membrane  or 
skin,  that  makes  each  air-cell,  does  not  let  the  blood 
come  through  it.  The  air  acts  upon  the  blood  through 
the  pores  of  the  skin,  and  of  the  capillaries  that  branch 
out  upon  this  skin.  It  is  by  the  airing  that  the  blood 
thus  takes,  that  every  drop  of  dark  blood  that  goes  to 
the  lungs  is  changed  to  red  blood. 

4.  The  great  object  of  the  machinery  of  respiration 
is  to  keep  the  air  going  into  and  out  of  these  air-cells. 
In  this  way  fresh  air  is  continually  brought  to  the 
blood.     When  you  breathe  in,  the  air  is  forced  into 
all  these  cells ;  and  when  you  breathe  out,  it  is  forced 
out  of  them.     It  is  not  all  forced  out.     The  lungs  are 
never  wholly  empty  of  air.     Enough  is  forced  out  to 
keep  the  air  in  the  lungs  constantly  changing. 

5.  Fig.  26  will  give  you  some  idea  of  the  structure 
of  the  lungs.     At  d  is  the  left    lung,  and  at  c  are  re- 
presented the  main  branches  of  the  windpipe  that  go 
to  the  right  lung,  separated  from  the  lung  itself.     At 
the  lower  part,  at  <?,  are  represented  the  very  minute 
branches  as  they  go  to  the  air-cells.    At  b  is  the  wind- 
pipe, and  at  a  is  the  larynx,  or  Adam's-apple,  as  it  is 
commonly  called.     It  is  through  a  chink  in  this  that 
the  air  passes  in  and  out  as  we  breathe. 

6.  I  will  now  show  by  what  machinery  the  air  is 
forced  into  the  lungs  and  out  of  them,  and  how  it 
operates.     You  see   that  as  you   breathe  the  chest 

How  does  the  air  act  upon  the  blood  in  changing  it  1  What  does  the 
machinery  of  respiration  do  1  Are  the  lungs  ever  wholly  without  air! 
Describe  the  structure  of  the  lungs  by  Fig.  26. 


56  FIRST   BOOK   IN   PHYSIOLOGY 


moves.  "No  air  would  ever  enter  the  lungs  if  this 
movement  of  the  chest  were  not  made.  If  a  bank  of 
earth  should  fall  upon  a  man,  and  cover  his  whole 
body  but  leave  his  head  free,  the  pressure  of  the  earth 
upon  hi&  chest  would  prevent  its  moving.  And  so  he 
would  die  for  want  of  air  in  his  lungs,  unless  the  pres- 
sure were  removed. 

7.  When  we  breathe  m,  or  make  an  inspiration,  as 
it  is  called,  the  air  rushes  into  the  lungs,  for  the  same 
reason  that  the  air  rushes  into  the  bellows  when  the 
handles  are  moved  apart.  In  inspiration  the  space  in 
the  chest  is  enlarged,  just  as  the  space  in  the  bellows 
is  enlarged  when  the  handles  are  moved  apart.  And 
because  the  space  is  enlarged  air  rushes  in  wherever 

What  is  said  of  the  motion  of  the  chest  in  breathing  ?  What  is  in- 
spiration ?  Why  does  air  rush  into  the  lungs  in  inspiration  ? 


RESPIRATION.  57 


it  can  get  in.  In  the  bellows  it  comes  in  through 
both  the  nose  and  the  hole  in  the  side.  In  the  chest 
it  comes  in  only  through  the  trachea  or  windpipe. 

8.  In  expiration,  that  is,  when  we  breathe  out,  the 
air  is  forced  out  through  the  trachea,  for  the  same 
reason  that  the  air  is  forced  out  through  the  nose  of 
the  bellows  when  you  press  the  sides  together  with 
the  handles.     In  forcing  the  air  out  of  the  lungs  the 
muscles  about  the  chest  do  for  the  chest  what  your 
hands  do  for  the  bellows. 

9.  If  the  bellows  had  no  hole  in  the  side,  and  the 
space  in  them  were  filled  with  a  soft  spongy  sub- 
stance, so  that  the  air  coming  in  through  the  nose 
would  go  into  all  the  spaces  in  this  substance,  the 
bellows  would  then  resemble  very  much  the  chest 
with  the  lungs.     In  Figs.  27  and  28  is  represented  a 

FIG.  27. 


pair  of  bellows  thus  arranged.  In  Fig.  27  the  sides 
of  the  bellows  are  brought  near  together,  and  so  some 
of  the  air  is  forced  out,  and  the  spaces  or  air-cells  are 
small.  So  when  expiration  is  performed  by  the  chest 

Give  the  illustration  of  the  bellows.     What  is  expiration  ? 
3* 


58  FIRST   BOOK    IN    PHYSIOLOGY. 

the  air-cells  shrink  as  the  air  passes  out  of  the  trachea. 
In  Fig.  28  the  sides  of  the  bellows  are  moved  apart 
and  the  air-cells  are  enlarged,  the  air  rushing  in 
through  the  nose  to  fill  them  up.  Just  so,  when  the 
chest  expands  in  inspiration,  the  air-cells  in  the  lungs 
enlarge,  and  the  air  fills  them  by  rushing  in  through 
the  trachea. 

10.  That  you  may  understand  how  the  movements 
of  the  chest  are  made  in  inspiration  and  expiration,  I 


must  describe  to  you  the  structure  of  the  chest.  Its 
walls  are  made  up  of  bones  connected  together  chiefly 
by  muscles.  The  bones  that  form  the  framework  of 
the  chest  you  see  in  Fig.  29.  The  spinal  column  ~b  b 
is  the  grand  pillar  that  supports  this  barrel-shaped 

Give  in  full  the  illustration  of  breathing  presented  in  Figs.  27  and  28. 


RESPIRATION.  59 


framework.  The  ribs  c  c  c  are  fastened  very  strongly 
by  ligaments  to  the  spinal  column.  They  are  twenty- 
four  in  number,  twelve  on  each  side.  They  extend 
round  towards  the  breast-bone  #,  in  front. 

11.  The  ribs  do  not  join  directly  to  the  breast-bone, 
as  you  can  see  in  the  Figure.  There  are  pieces  of 
cartilage,  or  gristle,  as  it  is  commonly  called,  that 
connect  them  to  the  breast-bone.  The  object  of  this 
is  plain.  If  the  ribs  extended  to  the  breast-bone, 
they  would  break  very  easily,  if  they  were  struck. 
But  the  cartilages  give  a  little,  as  it  is  expressed,  when- 
ever the  chest  receives  a  blow,  and  so  the  ribs  are 
seldom  broken. 

FIG.  30. 


I.  ; 
jmB^L 


Describe  the  framework  of  the  chest  How  many  ribs  are  there  ? 
How  are  the  ribs  connected  with  the  breast-bone  ?  What  is  the  object 
of  this  arrangement? 


60 


FIRST   BOOK    IN    PHYSIOLOGY. 


12.  This  framework  of  the  chest  is  connected 
together,  as  I  have  already  said,  chiefly  by  muscles. 
It  is  these  muscles  that  work  the  chest  in  the  move- 
ments of  breathing.  The  principal  muscle  that  acts 
in  breathing  ds  called  the  diaphragm.  It  is  a  stout 
muscular  and '  tendinous  sheet,  extending  across  the 
lower  part  of  the  chest.  It  is  the  wall  that  separates 
the  cavity  of  the  chest  from  the  cavity  of  the  abdo- 
men. Above  it  are  the  heart  and  the  lungs,  and 
below  it  are  the  stomach,  the  liver,  the  intestines,  &c. 
It  is  represented  in  Fig.  30.  Here  you  have  the  cav- 
ity of  the  chest,  Cc,  laid  open,  the  ribs  being  cut 
away  in  front,  and  the  heart  and  lungs  taken  out ;  D  D 
is  the  diaphragm.  It  is  fastened  to  the  spinal  column 
behind,  to  the  breast-bone  in  front,  and  to  the  lower 
ribs  all  around  the  sides.  You  see  that  it  is  not  flat, 

but  is  arched  upward. 

13.  I  will  now  show  you 
how  the  diaphragm  acts  in 
respiration.  You  can  see  that 
if  the  fibres  of  the  diaphragm 
contract  or  shorten  them- 
selves, it  will  not  be  arched 
up  so  high,  and  so  there  will 
be  more  room  in  the  chest. 
The  air,  therefore,  will  rush  in 
through  the  windpipe,  just  as 
it  rushes  into  the  bellows  when 
you  move  the  handles  apart. 
This  I  will  make  clear  to  you 

How  is  the  framework  of  the  chest  connected  together  ?  Describe 
the  diaphragm  ?  What  are  above  and  what  are  below  it  ?  To  what  ia 
it  fastened  ?  What  is  its  shape  ? 


FIG.  31. 


RESPIRATION.  61 


by  Fig.  31.  Let  a  represent  the  spinal  column,  5  the 
front  wall  of  the  chest,  Co  the  cavity  of  the  chest, 
and  Ca  the  cavity  of  the  abdomen.  At  d  is  repre- 
sented the  diaphragm.  You  see  that  if  the  fibres  of 
the  diaphragm  are  shortened,  so  as  to  flatten  its  arch 
down  to  the  line  0,  the  room  in  the  chest  will  be  very 
much  increased.  This  is  what  takes  place  every 
time  that  you  make  an  inspiration  or  draw  in  a  breath. 
When,  on  the  contrary,  you  make  an  expiration,  or 
force  out  the  breath,  the  diaphragm  is  pushed  upward, 
as  at  d,  and  so  the  room  in  the  chest  is  lessened. 

14.  If  when  you  draw  your  breath  in,  you  will 
place  your  hand  on  the  abdomen,  you  will  perceive 
that  it  presses  outward.     This  is  because,  as  the  arch 
of  the  diaphragm  is  flattened  in  inspiration,  the  con- 
tents of  the  abdomen  are  all  pressed  down  by  it.    But 
when  you  force  out  the  breath  from  the  lungs  the 
abdomen  moves  inward.    For  in  expiration,  the  stom- 
ach, liver,   &c.,  are  moved  upward,   and  they  push 
up  the  arch  of  the  diaphragm. 

15.  Commonly  the   diaphragm  does  most  of  the 
work  in  breathing.     But  there  are  other  muscles  that 
assist  a  little  generally,  and  sometimes  assist  very 
much.    They  are  muscles  that  move  the  whole  frame- 
work of  the  ribs  and  the  breast-bone  forward  and 
upward.     By  doing  this  they  enlarge  the  room  in  the 
chest  in  front  and  at  the  sides  at  the  same  time  that 
the  diaphragm  does  below.     Whenever  you  see  the 


Describe  by  Fig.  31  the  manner  in  which  the  diaphragm  acts.  Why 
does  the  abdomen  move  outward  in  inspiration  and  inward  in  expira- 
tion ?  What  muscles  assist  in  breathing?  Do  these  muscles  act  much 
ordinarily  ? 


62  FIRST    BOOK    IN    PHYSIOLOGY. 

chest  heaving  from  severe  exercise,  or  from  difficulty 
of  breathing,  in  disease,  these  muscles  are  acting 
strongly,  moving  the  ribs  and  the  breast-bone  upward 
and  forward. 

16.  I  said  in  the  first  part  of  this    chapter,    §  3, 
that  the  dark  blood  that  comes  to  the  lungs  is  changed 
to  red  blood  in  the  air-cells.     And  you  can  see,  from 
what  you  have  learned  in  this  and  in  the  last  chapter, 
how  important  it  is  that  this  change  in  the  blood 
should  be  well  and  thoroughly  accomplished.     If  the 
blood  is  not  changed  at  all,  death  results  at  once ;  for 
the  dark  blood  is  a  deadly  poison  to  all  the  organs,  if 
it  goes  to  them  in  the  arteries  and  gets  into  the  capil- 
laries.    Life  cannot  go  on  without  red  blood  is  con- 
tinually sent  to  the  organs.     This  is  the  reason  that 
life  is  so  soon  destroyed  in  drowning.    ~No  air  can  get 
into  the  lungs,  and  the  air  that  is  there  is  soon  used 
up.     The  blood  that  comes  to  the  lungs  very  soon 
therefore  ceases  to  be  changed,  and  so  dark  blood 
goes  to  the  brain  and  all  the   other  organs,  the  ma- 
chinery all  stops,  and  life  ceases. 

17.  Life  is  destroyed  in  drowning,  then,  in  the  same 
way  that  it  is  when  a  cord  is  tied  tightly  around  the 
throat.    It  is  destroyed  by  keeping  the  air  from  going 
into  the  lungs,  and  not  by  having  water  get  into  them, 
as  is  very  commonly  supposed.     Disease  often  produ- 
ces  death   by   keeping  the  air  from  getting  freely 
into  the  air-cells  of  the   lungs.     The  disease   called 
croup,  sometimes   so   blocks   up   the   windpipe  that 

"Why  is  it  so  important  that  the  dark  blood  should  be  changed  to  red 
in  the  lungs  ?  How  is  life  destroyed  in  drowning  ?  How  does  disease 
often  produce  death  ? 


RESPIRATION. 


very  little  air  can  get  through  it  into  the  lungs,  and 
so  it  destroys  life,  because  the  blood  cannot  be 
changed  anything  like  as  much  as  is  needed. 

18.  Life  has  been  sometimes  destroyed  by  confining 
too  many  persons  together  in  one  apartment.     The 
difficulty  here  is  really  the  same  as  in  drowning.     It 
is  the  want  of  air.     Death  occurs,  because  from  the 
want  of  air  the  blood  ceases  to  be  changed  in  the 
lungs.     I  could  cite  many  interesting  cases  of  this 
character,    but   I   will  give  you   but  one.     A  ship, 
called  the  Londonderry,  had  a  large  number  of  emi- 
grants on  board.     A  storm  arose,  and  all  the  passen- 
gers  were   ordered   to   go  below.     They  were  very 
much  crowded,  and  all  the  air  which  they  breathed 
came  to  them  through  the  hatchway,  an  opening  in 
the  deck.     But  as  the  sea  dashed  over  the  vessel,  the 
water  poured  down  this  opening.    The  captain,  there- 
fore, had  a  tarpaulin  (a  cloth  through  which  neither 
water  nor  air  can  pass)  nailed  over  it.    The  result  was 
that  a  large  number  of  the  emigrants  died  for  want 
of  air.     Their  cries  of  distress  could  not  be  heard  from 
the  noise  of  the  storm,  but  a  strong  man  at  length 
forced  a  hole  through  the  tarpaulin,  and  told  the  cap- 
tain that  the  people  were  dying.     The  tarpaulin  was 
torn  off,  and  thus  many  of  them  were  saved. 

19.  If  fresh  air  is  so  absolutely  necessary  to  life, 
then  the  health  of  the  body  must  be  injured,  when, 
from  day  to  day,  the  lungs  do  not  breathe  enough  of  it. 
One  sometimes  feels  very  languid  in  a  crowded  assem- 

What  is  said  of  death  being  sometimes  produced  by  a  want  of  ventil- 
ation ?  Relate  the  case  stated.  How  is  the  health  injured  by  deficient 
ventilation,  suffered  from  day  to  day  ? 


64  FIRST   BOOK   IN   PHYSIOLOGY. 

bly.  This  is  because  enough  good  fresh  air  does  not 
get  into  the  lungs,  and  the  work  of  changing  the 
blood  in  them  is  therefore  not  well  done.  Now  if 
this  work  is  poorly  done  in  the  lungs  every  day,  the 
blood,  the  building  material  of  the  body,  will  not  be 
as  good  as  if  the  lungs  did  their  work  well.  The  con- 
sequence will  be  that  the  building  and  the  repairing 
will  be  poorly  done.  In  other  words,  the  body  will 
not  be  vigorous,  and  will  be  liable  to  disease.  Living 
in  small  or  crowded  apartments  often  does  much 
harm  in  this  way. 

20.  There  is  another  way  besides  those  that  I  have 
mentioned,  in  which  the  air  can  be  prevented  from 
getting  to  the  lungs.     The   air-passages   may  all  be 
open,    and  there  may  be  plenty  of  air,   but  if  the 
muscles  of  the  chest  cannot  act,  no  air  can  go  into  the 
lungs  through  the  windpipe.    The  air,  you  remember, 
goe's  in  only  because  the  space  in  the  chest  is  enlarged 
by  these  muscles.     If  then  these  muscles  are  in  any 
way  prevented  from  acting,  the  air  will  be  kept  out 
from  the  lungs,  and  the  person  will  die  for  want  of 
air,  just  as  he  does  when  water  or  anything  else  shuts 
up  the  passages  to  the  lungs. 

21.  Life  is  not  very  often  destroyed  in  this  way.    It 
is  sometimes,  however,  and  I  have  already  alluded  in 
this  chapter  to  a  case  of  this  kind.     I  mean  the  case 
spoken  of  in  §  6,  of  a  man  with  a  bank  of  earth  fallen 
upon  him.     In  such  a  case  death  is  caused  very  much 
in  the  same  way  that  it  is  in  drowning.     In  both 
cases  air  is  prevented  from  getting  into  the  lungs, 

What  happens  if  the  muscles  of  the  chest  cannot  act  1    How  does 
death  occur  in  such  a  case  ? 


RESPIRATION.  65 


though  in  a  different  way  in  each  ;  the  blood  is  there- 
fore not  changed  from  dark  to  red ;  dark  blood  goes 
to  the  organs  of  the  body ;  these  organs  stop  work, 
for  want  of  red  blood,  and  life  therefore  ceases. 

22.  Though  life  is  not  often  destroyed  suddenly  by 
pressure  on  the  chest,  it  is  in  many  cases  destroyed 
gradually  by  this  pressure.     A  great  pressure,  as  you 
have  seen,  causes  death  at  once,  by  keeping  out  the 
air  entirely ;  but  a  small  pressure  prevents  the  lungs 
from  getting  as  much  air  as  is  needed,  and,  although 
this  does  but  little  harm  at  any  one  moment,  by  being 
continued  a  long  time  it  will  injure  the  health  and 
shorten  life. 

23.  That  you  may  understand  just  how  this  contin- 
ued small  pressure  does  harm,  call  to  mind  the  way 
in  which  the  blood  is  changed  in  the  lungs.     It  is 
done,  as  I  told  you  in  §3,  in  the  air-cells.     Each  one 
of  these  cells  has  to  do  its  share  of  the  work.   It  must 
change  the  blood  that  comes  to  it.     And  that  it  may 
do  this,  the  air  must  go  in  and  out  of  it  freely.     But 
this  cannot  be  if  the  chest  cannot  be  well  expanded. 
Pressure  on  it  will  keep  the  air  from  going  as  freely 
into  the  cells  as  it  should,  and  so  the  blood  cannot  be 
as  thoroughly  changed  as  is  necessary  to  make  it  good 
material  for  building  and  repairing.     The  blood  is 
poor  blood,  and  therefore  the  vigor  of  the  body  is 
lessened  and  the  health  is  injured. 

24.  Continued  pressure  around  .the  chest  does  harm 
in  another  way  also.     The  lungs,  like  any  other  ma- 
chinery, cannot  keep  in  good  condition  unless  they 

What  effect  is  produced  by  a  small  but  long-continued  pressure  on  the 
chest  ?     Explain  how  this  effect  is  produced 


66  FIRST   BOOK   IN   PHYSIOLOGY. 

work  freely.  If  they  are  continually  pressed  upon, 
so  that  they  cannot  expand  freely  as  they  take  in  the 
air,  the  tubes  and  cells  get  clogged  here  and  there 
from  time  to  time.  The  difficulty  is  not  noticed  per- 
haps for  a  long  time,  but  at  length  the  lungs  become 
manifestly  diseased.  You  see,  then,  that  a  continued 
pressure  of  the  chest  does  harm  in  two  ways.  1st,  It 
does  harm  to  the  whole  body,  because  it  makes  the 
blood  poor.  2d,  It  does  special  harm  to  the  lungs 
themselves. 

25.  If  the  chest  is  pressed  continually  while  the 
lungs  are  growing,  they  will  not  be  large  enough  to 
do  the  work  that  is  needed.     You  have  seen  that  in 
the  building  and  repairing  of  the  body  the  digestive 
machinery,  the  circulating  machinery,  and  the  ma- 
chinery of  the  respiration,  each  has  its  own  work  to 
do.     JSTow  if  any  one  of  these  sets  of  machinery  is 
cramped  and  small,  it  will  not  do  its  share  of  the  work 
well,  and  the  body  will  be  poorly  built.     When  the 
chest  is  pressed  upon  during  the  growth  of  the  body, 
the   breathing   machinery  is  cramped  and   is   made 
small.     There  are  not  air-cells  enough  to  change  all 
the  blood  that  the  body  needs  as  it  grows.     It  there- 
fore will  not  grow  well.     It  will  not  be  strong. 

26.  The    chest   is  often    much  pressed    by   tight 
clothing  while  the  body  is  growing.     The  lungs  are 
in  this  way  made  to  be  very  much  smaller  than  they 
should  be.    In  Figs.  32  and  33  you  see  this  illustrated. 
In  Fig.  33  is  represented  the  chest  of  its  natural  size. 

In  whatf  two  ways  does  pressure  on  the  chest  do  harm  ?  What 
happens  if  the  chest  is  pressed  continually  during  the  growth  of  the 
body? 


RESPIRATION. 


67 


.  32. 


FIG 


In  Fig.  32  you  see  the  chest  as  it  is  in  one  that  has 
been  girt  round  tightly  all  her  life,  so  as  to  make  her 
waist  very  small.  The  ribs,  you  see/  are  brought 
very  near  together,  so  that  they  could  hold  only  very 
small  lungs.  Health  and  vigor  cannot  exist  with 
such  small  breathing  machinery.  They  are  sacrificed 
in  such  cases  for  the  sake  of  a  small  waist. 

27.  In  China,  instead  of  a  small  waist,  a  small  foot 
is  considered  very  desirable  in  a  female.  The  foot  is, 
therefore,  put  under  pressure  while  it  is  growing,  just 
as  the  chest  often  is  among  us.  And  it  is  astonishing 
how  small  and  into  what  a  shape  it  can  be  made  to 
FIG.  34.  FIG.  ss.  grow.  In  Fig.  34:  is  a  side 

view  of  a  Chinese  lady's  foot. 
In  Fig.  35  is  a  view  of  the 
sole  of  the  same  foot.  You 
see  that  all  the  toes  but  the 
great  one  are  turned  in  under 
the  foot.  We  laugh  at  the  folly  of  the  Chinese,  but 
the  folly  of  one  that  cramps  the  chest,  as  represented 

Compare  the  compression  of  the  chest  with  the  compression  of  the 
feet  as  practiced  in  China. 


68  FIRST   BOOK   IN   PHYSIOLOGY. 

in  Fig.  33,  is  greater,  because  the  lungs  are  much 
more  important  organs  than  the  feet. 

28.  I  have  told  you  that  the  blood  is  changed  in 
the  lungs  from  a  dark  to  a  red  color.     You  have  been 
perhaps  curious  to  know  what    other  change  takes 
place  in  it  at  the  same  time.  It  is  very  much  changed 
in  its  composition.    And  the  air  in  changing  the  blood 
is  changed  itself.     The  air  that  you  breathe  out  is  not 
the 'same  as  that  which  you  breathe  in.     When  you 
breathe  in,  it  is  fresh  air  that  goes  into  the  lungs ; 
but  when  you  breathe  out,  the  air  that  comes  from 
your  lungs  is  partly  a  gas  or  air,  called  carbonic  acid 
gas.     This  gas  you  cannot  live  in  as  you  do  in  the  air 
that  is  all  around  you.     ISTo  animal  can  live  in  it. 

29.  If  you  should  put  a  bird  into  a  jar,  and  cover  it 
over  with  a  bladder  tightly,  so  that  no  air  can  get  in 
or  out,  the  bird  would  breathe  a  little  while  and  then 
would  die.     The  explanation  is  this :  The  bird  uses 
up  the  air  in  the  jar,  and  the  carbonic  acid  gas  which 
he  breathes  out  takes  the  place  of  the  air.     So  it  was 
with  the  passengers  in  the  cabin  of  the  Londonderry, 
mentioned  in  §  18.     The  cabin,  with   the  tarpaulin 
nailed  down  over  the  hatchway,  was  to  them  as  the 
jar  with  the  bladder  tied  over  it  is  to  the  bird.    They, 
like  the  bird,  used  up  the  air,  and  the  carbonic  acid 
gas  which  they  breathed  out  from  their  lungs,  took  its 
place  in  the  cabin,  as  the  carbonic  acid  gas  from  the 
lungs  of  the  bird  takes  the  place  of  the  air  in  the  jar. 

30.  This  carbonic  acid  gas  is  carbon  or  charcoal 

What  is  said  of  the  change  of  the  blood  in  the  luugs  ?  What  is  the 
difference  between  the  air  that  you  breathe  in,  and  that  which  you 
breathe  out  ?  Explain  the  experiment  with  the  bird. 


RESPIRATION. 


united  with  a  gas  called  oxygen.  The  amount  of  this 
carbonic  acid  gas  that  you  breathe  out  from  your 
lungs  in  the  course  of  a  day  is  such  that  it  contains 
several  ounces  of  charcoal.  This  gas  comes  from  the 
blood  in  the  lungs  as  it  changes  from  dark  to  red 
blood.  At  the  same  time  a  part  of  the.  air  that  we 
breathe  in  is  united  with  the  blood.  The  air  is  com- 
posed of  two  gases,  called  oxygen  and  nitrogen.  It 
is  the  oxygen  that  unites  with  the  blood. 

31.  You  see,  then,  that  a  sort  of  exchange  is  made 
in  the  lungs.    The  blood  comes  there  from  all  parts 
of  the  body  full  of  carbonic  acid  gas.    This  it  lets  out 
in  all  the  air-cells,  so  that  it  can  be  breathed  out 
through  the  windpipe.     At  the  same  time  that  it  lets 
out  this  gas  it  takes  in  a  supply  of  oxygen.     It  is  this 
exchange  of  carbonic  acid  gas  for  oxygen  that  alters 
the  blood  from  dark  to  red  blood,  and  thus  fits  it  to 
be  used  again  in  nourishing  the  body. 

32.  As  all  animals  are  throwing  off  from  their  lungs 
carbonic  acid  gas,  and  are  taking  oxygen  into  the 
blood,  one  would  suppose  that  the  oxygen  in  the  air 
would  all  be  used  up,  and  that  we  should  have  car- 
bonic acid  gas  everywhere  in  its  place.     How  is  it 
that  it  is  not  so  ?     I  will  tell  you.    The  carbonic  acid 
gas  is  all  taken  away  by  the  leaves,  which  are  the 
lungs  of  plants.     At  the  same  time  the  leaves,  give 
out  oxygen.     The  leaves  then  do  just  the  opposite  to 
what  our  lungs  do.     They  discharge  oxygen  and  take 
in  carbonic  acid  gas,  but  our  lungs  discharge  carbonic 

What  is  the  carbonic  acid  gas  breathed  out  made  of  ?  From  what 
does  it  come  ?  What  part  of  the  air  unites  with  the  blood  ?  What  is 
the  exchange  made  in  the  lungs  ?  What  is  the  effect  of  this  exchange  ? 


70  FIRST   BOOK   IN    PHYSIOLOGY. 

acid  gas  and  take  in  oxygen.  An  exchange,  then,  is 
constantly  going  on  between  our  lungs  and  the  leaves. 
Our  lungs  give  them  carbonic  acid  gas,  and  they  give 
our  lungs  oxygen. 

33.  The  lungs  vary  much  in  different  kinds  of  ani- 
mals.    The  gills  of  the  fish  are  its  lungs.     But  how, 
you  will  ask,  does  the  fish  get  the  air  to  his  lungs 
while  he  is  in  the  water  ?     I  will  tell  you.     There  is 
always  some  air  in  the  water,  and  the  air  is  made  to 
act  upon  the  blood  in  the  fish's  gills  in  this  way :  The 
fish  makes  the  water  run  through  his  mouth,  and  then 
out  through  the  feather-shaped  gills.      And  as  the 
water  is   passing   out   through   them,  the   air   in   it 
changes  the  blood  in  the  fine  blood-vessels  spread  out 
there,  just  as  the  air  in  the  air-cells  of  our  lungs  acts 
on  the  blood  in  the  blood-vessels  that  are  in  them. 
The  fish  then  may  be  said  to  breathe  air  and  water 
together.     We  cannot  do  this,  because  our  lungs  are 
not  fitted,  as  the  lungs  or  gills  of  the  fish  are,  to  sepa- 
rate the  air  from  the  water.     We  should  be  drowned 
if  we  should  try  to  do  it.     And,  on  the  other  hand, 
the  fish  dies  when  he  is  taken  out  of  the  water,  be- 
cause his  lungs  are  not  fitted,  as  ours  are,  to  use  air 
alone.     He  must  have  his  air  mixed  up  with  water, 
or  it  is  of  no  use  to  him. 

34.  It  can  be  proved  by  experiment  that  it  is  the 
air  in  the  water  that  keeps  the  fish  alive.     If  a  fish 
be  put  into  a  glass  vessel  filled  with  water,  and  covered 
with  a  bladder  tied  over  it,  so  as  to  make  it  air-tight, 

Describe  the  exchange  that  takes  place  between  the  lungs  of  animals 
and  the  leaves  of  plants.  What  are  the  lungs  of  fishes  ?  How  do  they 
use  them  ?  Why  cannot  fishes  breathe  air  alone  ? 


RESPIRATION.  71 


the  iisli  will  soon  die,  because  it  will  soon  use  up  all 
the  air  that  is  in  that  little  quantity  of  water.  When 
we  speak,  then,  of  fishes  living  in  water,  it  is  not 
strictly  true — they  live  in  water  that  has  air  mixed 
with  it. 

35.  The  lungs  of  insects  are  mere  air-vessels  here 
and  there  in  different  parts  of  the  body.    You  can  see 
the  holes  opening  into  them  on  the  sides  of  the  insect. 
The  grasshopper  has  twenty-four  of  these  holes  in 
four  rows. 

36.  There  is  a  curious  arrangement  of  the  breath- 
ing machinery  in  birds.     They  have  sacs  or  bags  in 
different  parts  of  the  body  that  are  connected  by  tubes 
with  the  lungs.     These  they  make  use  of  in  flying. 
When  they  wish  to  fly  upward,  the  lighter  they  make 
themselves  the  better.    They  therefore  force  air  from 
the  lungs  into  these  sacs.     But  when  they  wish  to 
come  down  quickly  they  let  the  air  out  of  the  sacs. 
Birds  that  fly  very  higl^  or  are  long  upon  the  wing, 
have  many  of  these  sacs,  and  even  some  of  the  bones 
are  made  in  them  so  that  they  can  hold  air. 

37.  The  chief  use  of  the  machinery  of  the  respira- 
tion is,  as  you  have  seen  in  this  chapter,  to  bring  the 
air  to  the  blood  in  the  lungs,  that  it  may  purify  it  and 
fit  it  to  be  used  again.  But  the  Creator  almost  always 
makes  a  thing  useful  in  other  ways  besides  the  use 
for  which  it  is  particularly  designed.     This  is  true  of 
the  respiration.     This  is  made  use  of  in  man  and  in 
many  other  animals  for  the  production  of  the  voice. 

How  can  you  prove  that  it  is  the  air  ia  the  water  that  keeps  fishes 
alive  ?  What  are  the  lungs  of  insects  ?  What  peculiarities  are  there 
in  the  breathing  apparatus  of  birds  ?  What  is  the  chief  use  of  the  res- 
piration ?  What  is  another  use  of  the  respiration  ? 


72  FIRST   BOOK   IN   PHYSIOLOGY. 

38.  The  breathing  machinery,  then,  besides  being 
a  chemical  laboratory  for  changing  the  blood,  is  also 
a  musical  instrument.     I  will  spe"ak  of  the  different 
parts  of  this  instrument.     You  feel  in  the  upper  part 
of  your  throat,  in  front,  a  firm  body,  the  larynx,  com- 
monly called  Adam's-apple.     This  is  the  music-box  of 
the  instrument;  that  is,  it  is   the  place  where  the 
voice  is  made  whenever  you  speak  or  sing.    The  chest 
is  the  bellows  to  this  little  organ  in  the  throat.     It 
holds  the  air  in  its  lungs,  and  blows  it  out  through 
the  windpipe  into  this  music-box  to  make  the  voice. 

39.  The  voice  is  made  in  the  larynx  very  much  as 
sounds  are  made  in  other  musical  instruments.    It  has 
two  flat  cords  stretching  across  it,  and  the  air  comes 
out  between  them.     When  you  force  out  the  air  from 
the  lungs,  it  strikes  on  these  cords  and  a  sound  is  made, 
just  as  when  you  blow  on  a  clarionet  the  air  from 
your  mouth  makes  the  sound  by  striking  on  the  reed. 
It  is  the  vibration  or  shaking  of  the  cords  by  the  air 
that  makes  the  sound  of  your  voice.     You  can  see 
this  vibration  in  some  instruments  as  they  are  played 
upon.     You  can  see  it  in  the  strings  of  a  violin  as  the 
player  draws  the  bow  across  them.     And  the  air  does 
to  the    cords  of  the    music-box  in  your  throat  the 
same  thing  that  the  bow  does  to  the  violin.     It  makes 
them  vibrate.     You  can  see  this  vibration,  also,  if  you 
look  into  a  piano  while  some  one  is  playing  on  it,  and 
observe  the  strings  as  they  are  struck  by  the  keys. 

40.  The  air  is  passing  out  and  in  through  the  chink 

Describe  the  apparatus  of  the  voice.  How  is  the  voice  made  ? 
Trace  the  resemblance  between  the  apparatus  of  the  voice  and  musical 
instruments. 


RESPIRATION.  73 


between  the  cords  of  the  larynx  continually  as  you 
breathe.  But  it  does  not,  as  you  know,  always  pro- 
duce a  sound.  I  will  explain  to  you  why  it  is  that  a 
sound  is  sometimes  made  as  the  air  passes  through 
this  chink,  and  sometimes  is  not.  When  the  cords 
are  loose  they  do  not  make  any  sound.  They  are 
loose  when  you  merely  breathe.  But  when  you  speak 
or  sing,  they  are  tightened.  You  know  that  the  strings 
of  a  violin  must  be  stretched  tight,  or  they  will  give 
no  sound.  And  so  it  is  with  the  cords  of  your  larynx. 
When  you  whisper,  these  cords  are  loose,  and  the  air 
goes  quietly  by  them,  and  the  sound  is  made  by  the 
mouth  and  lips.  In  whistling,  also,  they  are  loose, 
and  the  sound  is  produced  by  the  air  as  it  passes 
through  the  lips. 

41.  There  are  little  muscles  that  tighten  the  cords 
of  the  music-box  in  your  throat  when  it  is  needed. 
When  you  are  merely  breathing,  these  muscles  do  not 
act.     But  when  you  speak  or  sing,  they  contract,  and 
thus  tighten  the  cords.     The  different  notes  of  the 
sound  depend  upon  the  degree  to  which  these  cords 
are  tightened.     When  the  note  is  a  high  one,  they  are 
tightened  very  much ;  but  when  the  note  is  a  low 
one,  they  are  tightened  but  little.     The  working  of  the 
little  muscles  in  tightening  these  cords  is  regulated 
by  the  mind  in  the  brain,  by  means  of  the  nerves  that 
go  to  them. 

42.  It  is  only  animals  that  live  in  the  air  that  have 
a  voice.     Fishes  have  none.     Some  animals  can  live 


Why  does  not  the  air  always  produce  a  sound  as  it  goes  back  and 
forth  through  the  cords  of  the  larynx  ?     By  -what  are  the  cords  of  the 
larynx  tightened  ?     How  are  the  different  notes  of  the  voice  produced ! 
4 


74  FIRST   BOOK    IN    PHYSIOLOGY" 

both  in  the  water  and  in  the  air.  This  is  the  case 
with  frogs.  If  you  watch  a  frog,  you  will  see  that  he 
makes  no  noise  while  under  water,  but  he  does  all  his 
croaking  when  he  puts  his  head  up  into  the  air. 

43.  Man  is  the  only  animal  that  can  talk  to  any 
extent  with  his  voice.  He  does  it  in  this  way  :  The 
sound,  being  made  in  the  larynx,  is  put  into  various 
shapes,  as  we  may  say,  as  it  comes  out  through  the 
mouth.  The  palate,  the  tongue,  the  teeth,  the  lips, 
&c.,  give  it  these  various  shapes.  This  is  what  is 
called  the  articulation  of  the  voice. 


CHAPTEE    YI. 

BUILDING  AND  REPAIRING. 

1.  WE  are  so  accustomed  to  see  plants  and  animals 
grow,  that  we  do  not  think  of  the  wonderful  processes 
by  which  growth  is  effected.    We  get  the  idea  in  our 
childhood,  that  growth  is  a  very  simple  thing.     But 
it  is  not  so.     It  is  very  complicated,  and  there  are 
many  things  about  it  that  are  very  mysterious. 

2.  Everything  which  grows  is  made.     Growing  is 
building.     There   must   be,  therefore,   something   to 
build  with — that  is,  a  building  material.     In  plants, 
the  sap  is  the  building  material ;  and  in  animals,  it  is 
the  blood.     Every  part  of  the  human  body  is  'built; 
and,  as  you  will  see  in  this  chapter,  there  are  every- 

What  animals  have  a  voice  ?  What  is  the  articulation  of  the  voice  ? 
Is  growth  a  simple  process?  What  is  growing?  What  is  the  build- 
ing material  in  plants,  and  what  in  animals  ? 


BUILDING    AND    REPAIRING.  75 

where   little   builders,   that   are  always   at  work  in 
building  or  in  repairing. 

3.  All  the  various  structures  of  the  body  are  made 
or  built  from  the  same  thing,  the  blood.     This  ap- 
pears very  wonderful,  when  we  observe  how  different 
from  each  other  some  of  these  structures  are.     For 
example,  how  different  are  the  white  hard  teeth  from 
the  soft  red  gums  that  surround  them,  and  yet  both 
are  made  from  the  blood. 

4.  That  you  may  see  how  great  is  the  variety  of  the 
structures   formed   out   of  the  blood,   I   will   direct 
your  attention  to  some  one  part  of  the  body.     Look, 
for  example,  at  the   eye.     Observe  how  many  and 
how  various  are  its  parts.     I  will  mention  most  of 
them.     They  are,  the  bony  socket ;  the  eye-lids  ;  the 
eye-lashes  ;  the  firm  white  coat  of  the  eye  ;  the  clear 
round  window  in  front ;  the  beautiful  iris  ;  the  three 
different  fluids  that  are  in  the  eye-ball ;  the  muscles 
that  move  the  eye;  the  cushion  of  fat  in  which  it 
rests ;    the   nerves ;    the   tear-gland,    &c.     All  these 
parts,  so  different  from  each  other,  are  made  from 
the  blood.     And  so  it  is  with  all  the  different  parts 
in  every  portion  of  the  body. 

5.  Not  only  are  all  the  structures  of  the  body  built 
from  the  blood,  but  the  vessels  that  carry  the  blood 
to  them,  and  the  heart  that  pumps  it  into  them,  are 
made  from  the  blood  that  they  contain.     This  is  not 
less  wonderful  than  it  would  be  to  have  the  pipes  of 
an  aqueduct  made  out  of  the  water  that  is  in  them. 

From  what  are  all  the  different  structures  in  our  bodies  formed  ?  Il- 
lustrate the  variety  of  structures  made  from  the  blood  by  the  parts  of 
the  eye.  What  is  said  of  the  blood-vessels  and  the  heart  ? 


76  FIRST   BOOK    IN   PHYSIOLOGY. 


6.  The  fluids  of  the  body,  as  well  as  its  structures, 
are  made  from  the  blood.     The  glands  that  secrete 
these  fluids  make  them  from  the  blood  that  flows 
through  them.     Thus  the  tear-glands  make  the  tears 
that   moisten   the  eye   from   the   blood.     The   liver 
makes  the  bitter  yellow  bile  from  the  blood  also. 
And  so  of  the  rest  of  the  glands.     Observe,  that  the 
glands  are  made  from  the  same  blood  from  which 
their  secretions  are  formed.     Thus  the  tear-gland  and 
the  tears  are  made  from  the  same  blood.    That  is,  the 
factory  is  built  with  the  very  material  from  which  it 
manufactures  its  product. 

7.  You  can  see  better  how  wonderful  it  is  that  all 
the  parts  of  the  body  are  made  from  one  common 
building  material,  if  I  compare  the  building  of  the 
body  to  the  building  of  a  house.     When  a  house  is 
built,  there  must  be  gathered  together  a  great  variety 
of  materials.     There  must  be  beams,  boards,  shingles, 
&c.,  and  nails  to  fasten  them  together.     There  must 
be  bricks  made  of  clay.    Lime  must  be  obtained  from 
one  place,  sand  from  another,  and  hair  from  another ; 
and  these  mixed  make  the  mortar  to  fasten  the  bricks 
together.     There  must  be  stone  for  steps  and  founda- 
tion,  and   various   other  purposes.     Glass   must   be 
obtained  for  the  windows,  and  paper  for  the  walls. 
A  variety  of  materials  is  required,  to  make  paints  of 
different  colors.     All  these  and  various  other  things 

I  must  be  collected,  to  build  a  house.     And  then,  to 
finish  the  house  after  it  is  built,  materials  are  needed 

What  is  said  of  the  fluids  and  the  glands  that  secrete  them  ?  Give 
the  comparison  between  the  building  of  the  body  and  the  building  of  a 
house. 


BUILDING   AND    REPAIRING.  77 

from  every  quarter,  to  provide  the  various  articles  of 
furniture,  as  carpets,  chairs,  sofas,  beds,  bureaus,  mir- 
rors, lamps,  &c. 

8.  Xow,  in  the  house  which  your  spirit  inhabits, 
the  body,  there  is  a  much  greater  variety  of  structure 
and  furniture  than  there  is  in  the  houses  that  man 
builds  ;  and  yet  all  of  it  is  built  of  the  same  material. 
Many  of  its  parts  differ  from  each  other  much  more 
than  the  different  parts  of  a  house.    It  would  be  pass- 
ing wonderful  if  bricks  and  boards  and  nails  were 
made  out  of  the  same  thing,  but  these  articles  are  not 
so  much  unlike  each  other  as  the  hair,  the  skin,  and 
the  teeth.     Some  of  the  parts  of  the  body  are  totally 
unlike  the  blood,  and  it  seems  impossible  that  they  can 
be  made  from  it.     It  would  seem  comparatively  easy 
to  make  the  red  muscles  out  of  the  blood,  but  it  is 
not  so  with  such  structures  as  teeth,  nails,  tendons, 
hair,  &c. 

9.  I  will  now  show  you  how  the  blood  is  used  as  the 
building  material  of  the  body,  and  what  are  the  work- 
men that  thus  use  it.    The  blood  is  not  used  for  building 
and  repairing  while  it  is  in  the  arteries,  nor  while  it  is  in 
the  veins,  but  only  while  it  is  in  the  capillaries.    The 
heart  sends  it  through  the  arteries  to  the  capillaries, 
that  it  may  be  used  there.     Then,  after  it  is  used,  it 
goes  back  to  the  heart  through  the  veins.     The  heart, 
and  the  arteries,  and  the  veins  are  therefore  simply 
an  apparatus  or  set  of  machinery  for  circulating  the 
building  material.     This  apparatus  may  be  called  the 

What  is  said  of  the  difference  between  the  structures  of  the  body  and 
the  blood  from  which  they  are  made  ?  Where  is  the  blood  when  it  is 
used  for  building  I  What  is  said  of  the  apparatus  of  the  circulation  ? 


78  FIRST    BOOK    IN   PHYSIOLOGY. 

common  carrier  of  the  body.  It  carries  the  building 
material  to  the  very  door,  as  we  may  say,  of  all  the 
little  builders  everywhere. 

10.  It  is  supposed  that  the  building  is  not  done  by 
the  capillaries  themselves.     These  merely  hold  the 
blood,  while  some  other  small  vessels,  called  forma- 
tive vessels,  use  it  to  build  with.     These  formative 
vessels  have  the  power  of  selecting  from  the  blood, 
while  it  is  passing  through  the  capillaries,  just  what 
they  need  to  make  the  different  structures.    Some  are 
bone-makers,  some  nerve-makers,  some  skin-makers, 
&c.     The  bone-makers  select  from  the  blood  what  is 
needed   to   make   bone,    the   nerve-makers   what   is 
needed  to  make  nerve  ;  and  so  of  all  the  various  tex- 
tures of  the  body. 

11.  Sometiirfts  the  formative  vessels  fail  to  make 
the  right  selection,  as  for  example,  when  bone  is  formed 
where  it  should  not  be.     Thus,  sometimes  in  aged 
persons,   the  arteries   become  here  and  there  bony. 
In  this  case  some  of  the  artery-makers  leave  off  their 
usual  business  and  go  to  making  bone.     Sometimes 
even  the  valve-makers  in  the  heart  do  this.     When 
warts  appear  upon  the  skin  it  is  because  the  skin- 
makers  at  those  places  leave  off  their  regular  business, 
and  make  something  else.    But  such  irregularities  are 
not  common.     Generally,  the  formative  vessels  very 
faithfully  adhere  to  their  regular  work,  as  we  may 
express  it,  and  choose  just  the  right  material  from  the 
blood,  as  it  passes  along  by  them  in  the  capillaries. 

By  what  vessels  is  the  building  of  the  body  done  ?  What  is  said  of 
the  selecting  power  of  these  vessels  ?  Illustrate  the  fact  that  they 
Bometinies  err  in  their  selection. 


BUILDING   AND    REPAIRING.  79 

12.  Each  set  of  formative  vessels  appear  to  work 
together,  as  if   there  was  some  kind  of  agreement 
between  them.     If  there  were   not  this   concert  of 
action  there  would  be  confusion.     The  different  parts 
would  not  be  properly  formed.     If  there  was  irregu- 
larity,  for    example,  among    the   bone-makers,    the 
bones  would  not  be  regularly  made.    There  would  be 
bunches,  and  sharp  points,  and  rough  places,  where 
there  is  now  smoothness  and  regularity. 

13.  This  concert  or  agreement  of  action  in  the  for- 
mative vessels,  is  seen  in  the  different  shapes  that  the 
same  kind  of  structure  takes  in  different  parts  of  the 
body.     Thus,  every  bone  differs  in  shape  from  every 
other  bone.    That  is,  every  set  of  bone-makers  have  a 
plan  of  their  own,  which  is  different  from  the  plan  of 
every  other  set.     For  example,  the  bone-makers  that 
make  the  knee-pan  have  a  very  different  plan  from 
another  set  in  the  same  neighborhood  that  make  the 
long  thigh-bone.     So  also  the  makers  of  any  muscle 
have  a  different  plan  from  the  makers  of  any  other 
muscle.     And  so  of  other  kinds  of  structures.     The 
formative  vessels  everywhere  act  upon  some  regular 
fixed  plan,  just  as  if  they  thought  it  out,  and  agreed 
together  as  to  what  they  would  do. 

14.  This  concert  of  action  is  so  perfect  in  each  set 
of  the  formative  vessels,  that  the  different  sets  do  not 
interfere  with  each  other  when  working  in  the  same 
neighborhood.     Each  set  keeps   at  work   commonly 
within  its  own  bounds,  and  does  not  encroach  upon  the 

What  would  result  if  there  were  not  a  concert  of  action  among  the 
formative  vessels  ?  How  is  this  concert  of  action  seen  in  the  different 
shapes  given  to  the  same  kind  of  structure? 


80  FIRST    BOOK    IN    PHYSIOLOGY. 

work  of  another  set.  Thus  the  tooth-makers  and  the 
gum-makers  never  interfere  with  each  other.  There 
are,  as  you  have  seen,  many  different  structures  in  the 
eye,  but  there  is  no  interference  between  the  different 
sets  of  workmen  in  constructing  the  eye  and  in  keep- 
ing it  in  repair.  The  builders,  for  example,  that  con- 
struct the  white  part  of  the  eye-ball  never  encroach 
upon  those  that  make  the  clear  window  in  front,  that 
fits  into  the  white  part,  as  the  crystal  of  a  watch  does 
into  the  case.  They  only  build  up  to  the  edge  of  this 
window  all  around,  as  if  they  agreed  to  build  along 
this  circular  line. 

15.  You  can  see  this  concert  of  action  very  curiously 
exhibited  in  the  formation  of  the  lips.     I  told  you  in 
chapter  II,  §  20,  that  the  red  covering  of  the  lips  is 
somewhat  like  both  the  skin  and  the  mucous  mem- 
brane that  lines  the  mouth,  and  yet  it  differs  from 
either  of  them.     The  lip-makers  then  are  between 
two  sets  of  workmen,  that  are  making  textures  some- 
what similar,  and  yet  they  keep  their  work  very  dis- 
tinct from  that  of  the  workmen  on  either  side.    They 
are  always  making  the  red  delicate  texture  of  the  lip, 
and  never  go  to  making  skin  with  the  skin-makers  on 
the  one  side,  or  mucous  membrane,  with  the  work- 
men on  the  other. 

16.  This  concert  of  action  in  the  formative  vessels 
is  beautifully  shown  in  the  increase  of  the  size  of  the 
different  parts  of  the  body,  as  the  child  grows  up  to 
manhood.     All  the  different  structures  in  any  part 

How  is  concert  of  action  seen  in  the  fact  that  the  different  sets  of  for- 
mative vessels  never  interfere  with  each  other  ?  Give  the  illustration 
in  regard  to  the  lips. 


BUILDING   AND   REPAIRING.  81 

keep  the  same  proportions  as  they  increase  in  size. 
For  example,  as  the  finger  of  the  child  grows  to  be 
the  large  finger  of  the  adult,  all  the  different  sets  of 
builders  do  just  the  right  amount  of  building.  The 
nail-makers  make  just  enough  nail,  the  skin-makers 
enough  skin,  the  bone-makers  enough  bone,  &c.  If 
the  builders  did  not  work  after  some  plan,  there  would 
be  too  much  of  one  structure  and  too  little  of  another, 
and  the  finger  of  the  man  would  not  be  like  the  finger 
of  the  child.  And  so  of  other  parts. 

17.  There  is  another  thing  to  be  noticed  about  this 
agreement  of  action  in  building  the  body.     There  are 
two  halves  of  the  body,  which  are  generally  just  alike. 
The  right  hand  is  like  the  left,  the  right  side  of  the 
face  is  like  the  left,  and  so  of  the  other  parts.     That 
is,  for  every  set  of  builders  on  one  side  of  the  body 
there  is  another  set  on  the  other  side,  working  after 
precisely  the  same  plan,  as  if  they  had  agreed  to  do 
so.     Sometimes  this  agreement  is  not  fully  carried 
out,  and  one  part  is  not  shaped  exactly  like  its  corres- 
ponding part  on  the  other  side.     Thus,  the  two  sets 
of  nose-makers  in  the  two  halves  of  this  organ  some- 
times do  not  work  exactly  after  the  same  pattern,  and 
there  is  some  irregularity,  perhaps  one-si dedness. 

18.  What  I  have  just  said  of  the  body,  as  being  made 
of  two  halves  just  alike,  is  not  true  of  all  the  organs 
within  the  body.    While  the  brain  has  two  halves  just 
alike,  this  is  not  true,  as  you  have  already  seen,  of  the 
lungs,  the  heart,  the  stomach,  the  liver,  &c.    But  each 


How  is  the  concert  of  action  in  the  formative  vessels  seen  in  the 
regular  growth  of  the  body?     How  is  it  seen  in  the  two  halves  of  the 
body  ?     Is  the  concert  always  perfect  ? 
4* 


82  FIRST   BOOK    IN    PHYSIOLOGY. 

of  these  organs  is  constructed  after  a  fixed  plan  of  its 
own,  and  the  formative  vessels,  in  constructing  it 
after  this  plan,  must  have  an  agreement  in  their  ope- 
ration. 

19.  From  all  that  I  have  said  in  the  last  few  para- 
graphs, it  appears  that  there  is  as  much  agreement  of 
action  among  the  formative  vessels  of  the  body,  as 
there  would  be  if  they  were  intelligent  workmen,  and 
worked  under  directing  leaders.     In  what  way  the 
Creator  makes  them  to  work  together  thus,  we  do  not 
understand.  * 

20.  There  is  not  only  building  going  on  in  every 
part  of  the  body,  but  there  is  repairing  also.     And 
they  go  on  together.     You  remember  that  I  said  in 
the  first  chapter,  that  the  machinery  of  the  body  is  in 
use  all  the  time  that  it  is  building,  or  rather  all  the 
time  that  it  is  changing  from  small  machinery  into 
large  machinery.     There  is  therefore  some  wear  from 
this  use,  and  hence  repairing  is  needed  all  the  time. 

21.  The  way  in  which  the  repairing  is  done  is  this. 
When  any  particles  in  any  part  become  useless,  they 
are  taken  out  of  the  way,  and  are  carried  off  in  the 
dark  blood.     At  the  same  time  the  formative  vessels 
take  new  particles  from  the  red  blood  in  the  capilla- 
ries,   and   put   them  in  the  place  of  those  that  are 
removed.    As  you  work  the  muscles,  some  of  the  par- 
ticles get  worn  out  and  useless,  and  so  they  are  carried 
off,  and  new  particles  are  put  in  their  places.     As 
your  mind  uses  the  brain  in  thinking  and  studying,  it 

What  organs  of  the  body  do  not  have  two  halves  just  alike  ?  How 
is  concert  of  action  shown  in  constructing  th«m  ?  Do  we  know  how  this 
concert  of  action  in  the  formative  vessels  is  produced  ?  What  is  said 
of  the  repairing  of  the  body  ? 


BUILDING   AND   REPAIRING.  83 

wears  out  some  of  the  particles  there,  and  they  are 
taken  away,  and  new  ones  are  supplied.  And  so  of 
other  parts  of  the  body. 

21.  In  this  way  there  is  a  change  going  on  continu- 
ally in  all  parts  of  the  body.     There  are  probably 
scarcely  any  particles  in  your  body  now  that  were 
there  when  you  was  born.     It  is  a  very  common  no- 
tion that  the  whole  body  changes  once  in  seven  years. 
But  this  is  not  so.     There  is  no  such  regular  period 
for  the  change.     As  long  as  any  particle  is  useful  in 
its  place  it  remains  there ;  but  when  it  becomes  use- 
less it  is  taken  up  and  carried  away. 

22.  The  change  is  more  rapid  at  some  times  than 
it  is  at  others.     You  know  how  very  fast  sick  persons 
sometimes  become  thin,  and  then  how  fast  they  gain 
flesh  when  they  begin  to  eat  again.     In  such  cases  a 
large  portion  of  the  body  is  entirely  changed  in  a 
very  short  time.     The  change  in  young  children  is 
sometimes  very  great.     They  become  so  poor  in  a  lit- 
tle time  that  the  loose  skin  hangs  upon  their  limbs  like 
clothes ;  and  then  when  the  disease  is  gone,  and  the 
appetite  returns,  the  limbs  soon  become  plump  again. 
Now  the  changes  which  you  see  so  plainly  in  such 
cases  are  going  on  all  the  time  slowly  and  quietly  in 
the  body.     Old  useless  particles  are  constantly  taken 
away,  and.  new  particles  put  in  their  places. 

23.  It  is  to  effect   these  constant  changes  in  the 
growth  and  repair  of  the  body  that  the  blood  is  in 
motion  everywhere.     If  these  changes  were  not  going 

Describe  the  way  in  which  the  repairing  is  done.  What  is  said  of 
the  change  that  is  occurring  in  all  parts  of  the  body  I  Is  this  change 
going  on  always  just  alike  ?  In  what  cases  is  it  very  rapid  ? 


84  FIRST   BOOK   IN   PHYSIOLOGY. 

on,  there  would  be  no  need  of  having  the  blood 
circulate.  In  some  animals  these  changes  are  stopped 
in  cold  weather,  and  the  blood  stops  moving.  Great 
multitudes  of  such  animals  as  frogs,  bats,  flies,  spiders, 
&c.,  go  into  retirement  in  the  autumn  to  sleep  through 
the  winter.  Their  bodies  remain  without  change  all 
this  time.  They  are  alive,  but  as  still  as  death.  The 
machinery  of  life  is  still,  and  so  there  is  no  wear  and 
tear.  There  is  therefore  no  repairing  to  be  done,  and 
so  there  is  no  need  of  having  the  blood  circulate.  And 
as  there  is  no  circulation  there  is  no  need  of  respira- 
tion. 

24:.  When  the  warm  weather  comes,  these  animals 
wake  up  from  this  state  of  torpor.  The  blood  begins 
to  move  again,  and  they  breathe,  so  that  the  air  can 
go  into  the  lungs  and  change  the  blood.  They  begin 
to  eat,  too,  so  that  some  new  blood  can  be  made.  A 
gentleman  who  was  curious  on  this  subject,  kept  some 
frogs  and  snakes  in  this  torpid  state  in  an  ice-house  for 
three  years  and  a  half,  and  then  revived  them  by 
bringing  them  out  into  the  warm  a'r.  r 

25.  I  have  said  that  the  useless  particles  that  come 
from  the  wear  and  tear  of  the  organs  in  their  daily 
use  are  taken  up  to  be  carried  away  in  the  dark  blood. 
I  will  now  show  you  how  this  waste  matter  is  disposed 
of.  There  are  various  ways  of  carrying  it  off.  Some 
of  it  is  discharged  by  the  lungs.  At  every  breath 
some  part  of  the  waste  matter  of  our  bodies  is  thrown 
off  from  the  lungs' in  the  form  of  carbonic  acid  gas,  as 

Why  is  the  blood  constantly  in  motion  everywhere  ?  What  is  the 
situation  of  some  animals  in  winter?  What  effect  does  the  warm 
weather  of  spring  produce  iu  them  ? 


BUILDING   AND    REPAIRING.  85 

you  learned  in  the  chapter  on  Respiration.  Other 
portions  of  the  waste  matter  are  removed  by  the  skin, 
others  by  the  kidneys,  others  by  the  liver,  &c. 

26.  The  waste  matter  is  all  sent  off  by  these  differ- 
ent organs,  each  doing  its  share,  and  in  its  own  way. 
Observe  how  it  is  done.     The  waste  matter  is  in  the 
blood.     Now  as  the  blood  goes  to  these  organs,  the 
lungs,  the  skin,  the  liver,  the  kidneys,  each  does  its 
duty  in  cleansing  the  blood  of  the  waste  matter.  And 
in  doing  this  each  organ  seems  to  have  the  power 
of  choosing  just  that  part  of  the  waste  that  it  is  its 
business  to  throw  off.     And  it  never  makes  a  mis- 
take, and  throws  off  good  particles  instead  of  bad 
ones.  But  we  know  that  these  organs  have  no  thought 
nor  knowledge,  and  therefore  cannot  choose.     And 
the  perfect  way  in  which  they  are  made  by  the  Builder 
of  our  bodies  to  do  their  duty  is  a  mystery  which  we 
cannot  understand.     Each  organ,  I  have  said,  has  its 
own  way  of  getting  rid  of  the  waste  matter.     For  ex- 
ample, it  is  thrown  off  in  the  lungs  in  the  air  that 
we  breathe  out,  while  by  the  skin  it  is  thrown  off 
in  a  very  different  form — in  the  perspiration. 

27.  The  skin  is  so  important  an  organ  in  throw- 
ing off  the  waste   of  the  body,  that  I  will  describe 
its  structure.     There   are  really  two  skins — a  thick 
inner  skin,  and  a  thin  outer  one,  called  the  scarf-skin. 
The  coloring  matter  of  the  skin  is  not  in  the  inner 
skin,  but  in  the  inner  layers  of  the  scarf-skin.     When 
the  skin  is  rubbed  off,  as  it  is  expressed,  it  is  only  this 

In  what  various  ways  is  the  waste  matter  of  the  body  disposed  of? 
Describe  the  manner  in  which  it  is  done.  What  is  said  of  the  selecting 
power  of  the  different  organs  in  getting  rid  of  the  waste?  Is  it  thrown 
off  in  the  same  form  from  the  different  organs  ? 


m 

86  FIRST   BOOK   IN    PHYSIOLOGY. 

scarf-skin  that  is  removed,  and  the  inner  skin,  called 
the  true-skin,  is  laid  bare.  It  is  the  scarf-skin  that  is 
raised  when  a  blister  is  applied. 

28.  The  true-skin  is  very  sensitive,  for  it  has  a  great 
number  of  nervous  fibres  in  it.     This  is  for  the  pur- 
pose of  having  the  skin  act  as  a  sentinel  for  the  inner 
organs.     If  the  skin  did  not,  by  its  nerves,  warn  of  the 
approach  of  danger,  these  organs  would  be  much  of  t- 
ener  injured  than  they  now  are.    The  scarf-skin,  which 
is  not  sensitive  at  all,  makes  a  soft  delicate  covering  for 
the  inner  sensitive  skin.     The  true-skin,  without  this 
covering,  would  look  badly,  and  would  feel  too  keenly. 
I  shall  say  something  more  about  the  skin  as  a  sensi- 
tive organ  in  the  chapter  on  the  Nervous  System. 

29.  The  perspiration  of  the  skin  is  in  two  different 
forms.     When  the  skin  feels  soft,  but  does  not  look 
moist,  there  is  a  moisture  going  from  it  all  the  time 
in  the  form  of  vapor.     This  is  called  insensible  per- 
spiration, because  we  cannot  see  or  feel  it.     If  you 
place  your  hand,  when  it  appears  dry,  upon  a  glass, 
and  hold  it  there  for  some  time,  the  glass  will  become 
moist  from  the  insensible  perspiration.     The  skin  is 
sometimes  covered  with  moisture,  perhaps  in  drops, 
as,  for  example,  after  brisk  exercise  on  a  warm  day. 
This  is  called  sensible  perspiration. 

30.  The  perspiration  is  separated  from  the  blood  in 
the  skin  by  innumerable   little   glands.     The  pores 
through  which  it  is  discharged  are  the  outlets  of  the 

Describe  the -structure  of  the  skin.  Where  is  the  coloring  matter  of 
the  skin  ?  "What  is  said  of  the  sensitiveness  of  the  skin  ?  What  is  the 
use  of  the  scarf-skin  ?  What  is  the  difference  between  sensible  and 
insensible  perspiration  ?  By  what  is  the  perspiration  formed  ?  What 
are  the  pores  of  the  skin  ? 


BUILDING   AND    REPAIRING.  87 

tubes  from  these  glands.  There  is  another  set  of 
glands  in  the  skin  that  separate  an  oily  fluid  from  the 
blood.  These  oil-factories  are  most  abundant  wherever 
the  skin  particularly  needs  oiling,  as  at  the  joints, 
where  one  part  of  the  skin  rubs  against  another,  and 
where  the  skin  is  exposed  to  the  air,  as  in  the  face. 

31.  The  skin  then  serves  several  different  purposes. 
1.  It  is  a  firm,  but  soft  and  beautiful  covering  for  the 
body.     2.  By  its  nerves  it  warns  of  the  approach  of 
danger.     3.  It  also,  by  its  nerves,  as  the  organ  of 
touch,  gives  knowledge  to  the  mind  of  objects  around 
us.     4.  It  discharges,  in  its  perspiration,  much  of  the 
waste  matter  of  the  body. 

32.  The  change  that  I  have  described  in  this  chap- 
ter, as  going  on  in  all  parts  of  the  body,  produces  to 
a  great  extent  the  heat  of  the  body.     It  does  this  by 
a  kind  of  combustion  or  burning.     You  remember, 
that  in  the  chapter  on  Respiration  I  told  you  that  the 
oxygen  of  the  air  enters  the  blood  in  the  lungs,  and 
goes  with  it  to  the  heart,  and  then  is  sent,  with  it,  all 
over  the  body.     Now,  this  oxygen,  when  it  comes  to 
the  capillaries,  is  united  to  carbon,  that  is,  charcoal, 
and  makes  carbonic  acid  gas.     This  gas  goes  to  the 
heart  with  the  dark  blood,  then  is  sent  with  it  to  the 
lungs,  and  there  is  thrown  off,  as  I  have  already  told 
you.     At  the  same  time,-  the  oxygen  also  unites  in  the 
capillaries  with  another  substance,  a  gas  called  hydro- 
gen.    It  is  this  union  of  the  oxygen  with  the  carbon 
and  the  hydrogen  that  makes  the  heat  of  the  body. 

33.  Xow  this  is  very  much  like  what  takes  place  in 

"What  other  glands  are  there  in  the  skin,  and  where  are  they  most 
numerous  ?  Mention  the  four  different  purposes  which  the  skin  serves. 
Describe  the  process  by  which  the  heat  of  the  body  is  chiefly  produced  ? 


88  FIRST   BOOK   IN  PHYSIOLOGY. 

combustion.  "When  we  burn  charcoal,  that  is,  carbon, 
in  the  air,  it  unites  with  the  oxygen  of  the  air ;  and 
it  is  this  union  that  makes  the  heat  that  is  given  out. 
So  too,  when  the  chemist  burns  oxygen  and  hydrogen 
gas  together,  it  is  their  union  that  produces  the  heat. 
So  it  is  in  the  capillaries  of  the  body.  The  union  of 
the  oxygen  with  the  carbon  and  the  hydrogen  makes 
the  heat  of  the  body.  There  is  a  fire,  then,  we  may 
say,  in  every  part  of  the  body  in  the  fine  blood-ves- 
sels, although  there  is  no  flame. 

34.  Carbonic  acid  gas  is  produced  by  the  burning 
of  charcoal  in  the  air.     So  also  it  is  produced  by  the 
fire  in  the  capillaries.     It  is  carried  from  them  with 
the  blood   to  the  lungs,  and  there  it  is  discharged 
through  the  windpipe.     The  windpipe  may  then  be 
called  the  smokepipe  or  chimney,  through  which  the 
smoke  of  this  general  combustion  in  the  body  is  let 
off  into  the  air.     It  will  be  interesting  to  notice  here 
that  the  windpipe  answers  three  different  purposes. 
1.  It  conducts  fresh  air  to  the  lungs.     2.  It  carries  off 
the  bad  air,  or,  as  we  may  express  it,  the  smoke  of 
the  fire  that  is  in  the  body.     3.  While  carrying  off 
the  bad  air  it  acts,  when  we  speak  or  sing,  as  the  con- 
ducting pipe  of  the  organ  of  the  voice  in  the  throat 
from  the  bellows  at  work  below,  the  chest. 

35.  Observe  that  in  this  combustion  of  the  capilla- 
ries a  part  of  the  fuel  is  furnished  from  the  waste  of 
the  body.     The  carbon  and  hydrogen  that  unite  with 
the  oxygen  are,  to  a  great  extent,  produced  by  this 
waste.     As  the  oxygen  comes  in  the  red  blood  to  the 

Trace  the  resemblance  between  this  and  the  process  of  combustion. 
What  three  purposes  does  the  windpipe  answer  ? 


BUILDING   AND   REPAIRING.  89 

capillaries,  the  useless  particles  that  are  to  be  thrown 
off  furnish  carbon  and  hydrogen  to  be  burned  with 
the  oxygen.  And  then  what  results  from  this  burn- 
ing is  carried  back  in  the  dark  blood  in  the  veins. 

36.  When  anything  is  burned  up  it  is  spoken  of  as 
being  destroyed,  but   this  is  not  so.     The  burning 
merely  changes  matter  into  some  other  form.     Thus, 
when  carbon  or  charcoal  is  burned  in  air,  the  oxygen 
of  the  air  is  taken  away,  and  the  charcoal  disappears. 
But  there  are  ashes  left,  and  a  quantity  of  carbonic 
acid  gas  has  been  formed.     So,  when  oxygen  and  hy- 
drogen are  burned  together,  they  both  disappear,  but 
in  disappearing  they  form  water.     The  same  thing  is 
true  of  the  combustion  in  the  body.     The  oxygen  and 
carbon  are  burned  up  together  in  the  capillaries  ;  but 
carbonic  acid  gas  results,  just  as  when  charcoal  is 
burned  in  the  air,  and  this  gas  is  carried  to  the  lungs, 
to  be  thrown  off  through  the  chimney,  the  windpipe. 
Oxygen  is  burned  up  also  with  hydrogen  in  the  capil- 
laries, and  water  results,  just  as  when  the  chemist 
burns  them  together.     Much  of  this  water  thus  form- 
ed is  thrown  off  by  the  lungs  in  vapor.    It  is  supposed 
that  a  man  discharges  from  his  lungs  in  this  way 
about  two  quarts  of  water  in  every  twenty-four  hours. 

37.  You  can  see  now  why  it  is  that  exercise  in- 
creases the  heat  of  the  body.     During  exercise  the 
heart  beats  quicker  than  usual,  and  so  sends  the  blood 
more  rapidljpeverywhere.     More  blood  passes  there- 


From  -what  does  the  fuel  for  the  combustion  in  the  body  mostly 
come  ?  Is  it  strictly  correct  to  speak  of  a  thing  as  being  destroyed  when 
it  is  burned  ?  What  are  the  products  of  the  combustion  in  the  capilla- 
ries i  What  becomes  of  these  products  ? 


90  FIRST    BOOK    IN    PHYSIOLOGY. 

fore  through  the  lungs.  The  breathing  is  quickened 
also,  and  as  more  air  is  taken  into  the  lungs,  of  course 
more  of  the  oxygen  of  the  air  unites  with  the  blood. 
But  the  oxygen  is  a  part  of  the  fuel  that  is  burned  in 
the  capillaries,  and  the  more  fuel  there  is  the  greater 
is  the  heat.  The  other  parts  of  the  fuel,  the  carbon 
and  the  hydrogen,  are  increased  also.  For  these  come, 
as  I  have  before  told  you,  from  the  waste  of  the  sys- 
tem, and  there  is  more  wear  and  tear,  and  therefore 
more  waste,  when  the  body  is  exercised  than  when  it 
is  quiet. 

38.  You  can  see,  also,   the  principal  reason  that 
some  animals  are  so  much  warmer  than  others.     You. 
have  often  heard  the  expression,  as   cold  as  a  frog. 
The  frog  belongs  to  that  class  of  animals  that  are 
called    cold-blooded.       These   cold-blooded    animals 
make  but  little  exertion,  and  so  there  is  but  little 
wear  and  tear  of  the  system.     There  is  therefore  but 
little  carbon  and  hydrogen  furnished  for  the  fire  in 
the  capillaries,  and  but  little  heat  is  made.     As  there 
is  so  small  a  quantity  of  carbon  and  hydrogen  to  be 
burned,  there  is  not  much  oxygen  required,  and  so 
the  breathing  is  performed  in  a  very  lazy  manner. 

39.  If  you  watch  a  frog  you.  will  see  that  he  exerts 
himself  but  little  in  comparison  with  warm-blooded 
animals,  as  birds,  for  example.     He  never  seems  to 
take  any  pleasure  in  exercise.     He  never  gambols. 
He  sits  still  when  he  can,  and  leaps  only  when  he  is 
obliged  to  do  it.     He  does  not  even  croak  but  seldom. 
But  to  the  bird  exertion  is  a  pleasure.     He  is  ever  on 

How  does  exercise  increase  the  heat  of  the  body  ?     What  is  the  chief 
cause  of  the  difference  between  warm  and  cold-blooded  animals  ? 


BUILDING    AND    REPAIRING.  91 

the  wing.  There  is  much  wear  and  tear,  therefore,  in 
his  system,  and  an  abundance  of  carbon  and  hydro- 
gen is  ready  to  be  burned  up  with  the  oxygen.  His 
blood  circulates  rapidly,  and  he  breathes  quickly  in 
order  to  supply  all  the  oxygen  that  is  needed.  And 
the  fire  which  thus  burns  so  briskly  in  all  his  capilla- 
ries makes  him  a  warm-blooded  animal. 

40.  A  good  supply  of  pure  air  is  necessary  to  ena- 
ble the  system  to  keep  up  its  heat.     The  reason  is, 
that  when  the  air  is  impure,  there  is  not  a  sufficient 
quantity  of  oxygen  supplied.     This  part  of  the  fuel 
being  deficient,  the  fire  is  low,  and  there  is  too  little 
heat. 

41.  The  supply  of  oxygen  is  often  deficient  from 
pressure  on  the  chest.     Those  whose  lungs  are  thus 
prevented  from  becoming  as  large  as  they  need  to  be, 
are  therefore  much  more  readily  affected  by  cold  than 
those   who   have  chests   of  the   proper  size.     They 
require   more  clothing  to   keep   them   warm.     The 
heat-making  power  in  them  is  lessened,  because  the 
lungs  that  take  in  that  important  part  of  the  fuej, 
oxygen,  are  not  capacious  enough.     And  this  lessen- 
ing of  the  heat-making  power  of  the  body  is  a  great 
source  of  disease. 

42.  It  is  only  in  a  vigorous  and  active  state  of  the 
body  that  the  proper  amount  of  heat  is  produced.    In 
a  state  of  vigor,  the  blood  is  rich  and  is  well-charged 
with  that  important  agent  of   combustion,    oxygen. 
And  when  the  body  is  active,  the  change  that  goes  on 

Give  the  comparison  made  in  relation  to  the  frog.  Why  is  a  free 
supply  of  air  necessary  to  keep  up  the  heat  of  the  body  ?  What  is  said 
of  pressure  on  the  chest  in  relation  to  animal  heat  ? 


92  FIRST   BOOK   IN   PHYSIOLOGY. 

briskly  everywhere  supplies  the  proper  quantity  of 
carbon  and  hydrogen  to  be  burned  with  the  oxygen 
in  the  capillaries. 

43.  The  body  needs  to  be  well  nourished  in  order 
to  maintain  its  heat.     For  its  vigor  depends  to  a  great 
extent   upon   its   nourishment.     The  poorly  fed  are 
weak,  and  are  easily  pinched   by  the   cold.     They 
have  not  enough  of  carbon  and  hydrogen  and  oxygen 
in  them  to  keep  up  a  good  fire  in  the  capillaries. 

44.  You   see,   then,    that   there   are   three   things 
needed  to  maintain  the  heat  of  the  body.     1.  A  full 
supply  of  fresh  air ;  2,  sufficient  exercise ;  and  3,  a 
due  amount  of  food.     If  there  be  a  deficiency  of  any 
one  of  these  three  things  the  body  will  be  weak  and 
easily  chilled. 

45.  There  are  some  kinds  of  food  that  make  more 
heat  than  others,  because  they  contain  more  carbon 
and  hydrogen ;  that  is,  more  fuel  for  burning  with 
the  oxygen.     Animal  food,  and  especially  that  which 
is  oily  or  fatty,  is  of  this  character.     This  is  the  rea- 
son that  more  of  this  kind  of  food  is  needed  in  winter 
than  in  summer.     It  is  the  reason  also  that  the  inhab- 
itants of  cold  climates  eat  more  meat,  and  especially 
fat  meat,  than  those  who  live  in  warm  climates.    The 
fat  and  oil  which  the  Greenlander  devours  in  such 
quantities  are  used  up  as  fuel,  to  keep  np  the  heat  of 
the  body,  in  the  midst  of  the  intense  cold  to  which  it 
is  exposed.     By  eating  largely  of  such  food,  he  can 

Why  are  vigor  and  activity  necessary  to  maintain  the  animal  heat 
properly  ?  What  is  said  of  food  ?  What  then  are  the  three  things 
needed  for  the  heat  of  the  body  ?  Are  all  kinds  of  food  alike  in  furnish- 
ing fuel  for  the  animal  heat  ?  What  is  said  of  food  in  relation  to  dif- 
ferent seasons  and  different  climates  ? 


BUILDING   AND   REPAIRING.  93 

get  along  with  less  clothing  than  he  would  otherwise 
require,  because  it  makes  so  much  heat. 

46.  The  carbon  and   hydrogen   that   are   burned 
with  the  oxygen,  are  not  furnished  wholly  from  the 
waste  particles  of  the  body.    Some  of  this  fuel  comes 
directly  from  the  food  we  eat,  when  the  waste  does 
not   afford   enough   of  it.     Some   of  it   also   comes 
from  the  fat  which  is  stored  up  here  and  there  in  the 
cellular  membrane  of  the  body.     When  we  are  sick, 
and  cannot  eat,  the  fat  lessens  very  rapidly,  being 
burnt  up,  as  we  may  say,  to  keep  the  body  warm. 
So  also,  when  an  animal  goes  into  winter-quarters, 
and  becomes  torpid,  or  hibernates,  as  mentioned  in 
§  23,  in  this  chapter,  he  is  kept  warm  in  this  state  by 
the  fat  in  the  body.     He  becomes  very  fat  in  the 
autumn ;  but  when  he  crawls  out  of  his  quarters  in 
the  spring  he  is  very  lean,  because  his  fat  has  been 
burned  up,  in  keeping  him  warm  through  the  winter. 

47.  In  this  chapter  I  have  shown  you  what  changes 
are  going  on  in  the  building  and  repairing  of  the 
body.     You  have  seen  that  waste  particles  are  every- 
where  constantly   taken   away,    and   new   ones   are 
deposited  in  their  places.     You  have   seen  that  in 
doing  this  the  blood  is  changed  in  the  capillaries  from 
red  to  dark  blood.     I  have  shown  you  that  this  is  a 
chemical  change,  and  so  every  little  capillary  is  a 
chemical  laboratory.     And  finally,  you   have   seen 
that  there  is  a  fire  in  each  one  of  these  laboratories, 
and  that  in  this  way  the  heat  of  the  body  is  chiefly 
maintained. 


What  two  other  sources  for  fuel  for  the  combustion  in  the  body,  are 
besides  the  waste  particles  ?     Give  the  summary  in  §  47. 


94  FIRST    BOOK    IN    PHYSIOLOGY. 

CHAPTER    VII. 

THE  NERVOUS  SYSTEM. 

1.  I  HAVE  thus  far  told  you  only  about  building  the 
body  and  keeping  it  in  repair.     You  have  seen  in  the 
previous  chapters  that  the  blood  is  the  common  build- 
ing material  of  the  body — that  it  is  the  office  of  the 
digestive  machinery  to  separate  from  the  food  the 
nourishing  part  of  it,  and  fit  it  to  become  blood — that 
the  circulating  machinery  circulates  the  blood  every- 
where, that  it  may  be  used  as  building  material — that 
the  formative  vessels,  the  real  builders  of  the  body, 
everywhere  use  it  to  build  and  repair — and  that  the 
machinery  of  the  respiration  keeps  the  blood  fresh 
and  in  good   condition,  by   continually  changing  it 
after  it  has  been  used  by  the  builders. 

2.  Digestion,    circulation,  respiration,   and   forma- 
tion, are  then  all  engaged  in  building  and  repairing 
machinery.     In  the  remaining  chapters  of  this  book 
I  intend  to  explain  to  you  the  uses  for  which  this 
machinery  is  built. 

3.  The  mind  uses  this  machinery.     First,  it  uses 
some  of  it  to  learn  what  is  going  on  around  it.     It 
uses  the  apparatus  or  machinery  of  the  eye  to  see 
with  ;  that  of  the  ear  to  hear  with  ;  that  of  the  nose 
to  smell  with ;  that  of  the  mouth  to  taste  with ;  and 
that  of  the  skin  to  feel  with.     In  all  these  cases  the 

Give  the  summary  of  subjects  treated  of  in  the  previous  chapters. 
What  are  to  be  the  subjects  of  the  following  chapters  as  stated  in  §  2  ^ 
What  uses  the  machinery  of  the  body  ?  For  what  purpose  does  the 
mind  use  the  machinery  of  the  senses?  Illustrate. 


THE   NERVOUS   SYSTEM.  95 

mind  is  acted  upon.  Light  acts  upon  it  by  means  of 
the  eye ;  sounds  act  upon  it  by  means  of  the  ear ; 
odors  act  upon  it  by  means  of  the  nose,  &c.  The 
mind  is  in  these  cases  passive.  It  receives  impressions. 

4.  But  secondly,  the  mind  is  in  an  active  state,  in 
using  some  of  the  machinery  of  the  body.     That  is,  it 
makes  impressions  upon  the  world  around.     It  does 
this  by  moving  the  muscles.     For  example,  it  moves 
the  muscles  of  the  voice,  and  thus  produces  sounds. 
It  works  the  muscles  of  the  face,  to  give  it  expression. 
It  sets  in  motion  the  muscles  of  the  arm  and  other 
parts  of  the  body,  when  we  work. 

5.  You  see,  then,  that  the  purpose  of  all  the  ma- 
chinery is   to   have   a  communication   between   the 
mind  and  all  that  is  around  it.     The  mind,  by  some 
parts  of  the  machinery,  makes  impressions,  and  by 
other  parts  receives  impressions.     And  you  see,  also, 
that  all  that  goes  into  the  mind  gets  there  by  means 
of  the  machinery  of  the  senses,  and  all  that  comes 
out  from  the  mind   comes  by  the  machinery  of  the 
muscles.     That  is,  all  the  knowledge  that  enters  the 
mind  enters  by  the  senses ;  and  the  mind  uses  this 
knowledge,  in  acting  upon  things  and  beings  around 
it,  by  means  of  the  muscles. 

6.  Xow  the  mind  makes  all  this  use  of  the  ma- 
chinery of  the  body  by  means  of  the  nervous  system. 
The  brain  is  the  great  centre  of  this  system,  and  here 
the  mind  has  its  seat.     And  the  mind  is  connected 
with   the   organs  of  the  senses  by  the  nerves  that 

In  what  state  is  the  mind  in  using  this  machinery  ?  In  using  what 
machinery  is  it  in  an  active  state  ?  Illustrate.  What  is  said  of  the 
communication  between  the  mind  and  the  world  around  it  ?  By  means 
of  what  does  the  mind  make  use  of  the  machinery  of  the  body  ? 


96  FIRST    BOOK    IN    PHYSIOLOGY. 

branch  out  from  the  brain,  and  go  to  'these  organs, 
It  receives  impressions  by  the  nerves  that  connect  the 
brain  with  the  organs  of  the  senses,  and  it  makes 
impressions  by  the  nerves  that  go  to  the  muscles. 

7.  The  brain  then  may  be  considered  the   great 
central  workshop  of  the  mind.     There  it  sits  and  ope- 
rates by  the  nerves  upon  all  the  machinery  of  the 
body.     It  receives  messages  by  one  set  of  nerves,  and 
sends  out  messages  by  another  set.     The  nerves  by 
which  it  receives  messages  are  called  nerves  of  sen- 
sation.    The  nerves  by  which  it  sends  out  messages 
are  called  nerves  of  motion.     You  can  see  how  this  is 
by  a  single  example.    If  you  put  your  finger  too  near 
the  fire,  you  feel  pain  in  it,  and  instantly  draw  it 
away.     Now  see  what  takes  place  in  this  case.     The 
sensation  made  by  the  fire  goes  by  the  nerves  of  sen- 
sation to  the  brain,  so  that  the  mind  feels  it ;  and 
then  the  mind  sends  a  message  or  order  by  the  nerves 
of  motion  to  the  muscles  of  the  arm,  and  they  draw 
the  finger  away. 

8.  We  know  that  the  nerves  are  the  means  of  this 
connection  between  the  mind  and  the  various  parts 
of  the  body  in  this  way.     If  the  nerves  of  any  part 
are  divided,  the  part  cannot  move,  and  there  is  no 
feeling  in  it.     For  example,  if  the  nerves  of  the  hand 
are  divided,  you  can  pinch  or  prick  it  without  pro- 
ducing any  feeling,  because  the  mind  has  lost  its  con- 
nection with  it.     And  the  muscles  of  the  hand  will 
not  act  if  the  mind  sends  a  message  to  them,  because 

What  is  said  of  the  brain  ?  What  of  the  nerves  of  sensation  and 
of  motion  ?  Give  the  illustration  in  §  7.  How  do  we  know  that  the 
nerves  are  the  means  of  communication  between  the  rnind  and  the  dif- 
ferent parts  of  the  body  ? 


THE    NERVOUS    SYSTEM.  97 

*> 

the  message  can  go  no  further  than  where  the  nerves 
are  divided,  just  as  when  a  telegraph  wire  is  broken, 
the  electricity  can  go  only  to  the  point  where  it  is 
broken. 

9.  The  nerves   are   white   cords.     Each  nerve   is 
made  up  of  a  great  number  of  tubes.    These  tubes 
are  so  small  that  they  can  be  seen  only  by  the  aid  of 
a  very  powerful  microscope.    Each  tube  is  altogether 
by  itself.     It  is  never  seen  to  communicate  with  any 
of  the  other  tubes  that  are  bound  up  with  it  in  the 
same  nerve.     Each  of  these  tubes  then  goes  by  itself 
from  the  brain,  where  it  begins,  to  the  place  where  it 
ends  in  the  body.     To  every  separate  fibre  of  any 
muscle  there  is  probably  one  of  these  tubes.     This  is 
the  telegraphic  wire  by  which  the  fibre  is  told  by  the 
mind   in   the  brain  to   act.     As  each  fibre  receives 
a  message  by  itself,  whenever  the  muscle  acts,  what 
a  multitude  of  messages  are  sent  to  the  whole  muscle ! 

10.  Some  of  the  tubes  in  the  nerves  are  for  sensa- 
tion, and  others  are  for  transmitting  the  messages  or 
impressions  to  the  muscles.    These  two  kinds  of  tubes 
are  very  commonly  bound  up  together  in  the  same 
nerve  to  go  to  any  part.     And  yet  they  are  entirely 
separate  in  their  office.     For  example,  in  the  great 
nerve  that  goes  to  the  arm,  the  nervous  tubes  for  the 
muscles  and  the  tubes  for  sensation  are  bound  up 
together.     But  as  the  nerve  branches  out  to  be  dis- 

o 

tributed,  the  two  kinds  of  tubes  are  separated.  And 
the  same  tube  never  transmits  sensation  to  the  brain 
and  brings  back  a  message  to  a  fibre  or  a  muscle. 


.. 


Of  what  are  the  nerves  composed  ?     Do  the  tubes  in  them  communi- 
together  ?     What  two  kinds  of  tubes  are  there  in  the  nervea? 
D 


98  FIRST    BOOK    IN    PHYSIOLOGY. 

The  sensation  goes  by  one  set  of  tubes,  and  the  mes- 
sages to  the  fibres  of  the  muscles  come  by  another  set. 

11.  In  the  body  and  in  the  limbs  the  two  kinds  of 
tubes  are  bound  together  in  the  same  nerves.     But  in 
the  face  the  two  kinds  of  tubes  are  in  two  separate 
sets  of  nerves.     There  we  have  nerves  of  sensation 
and  nerves  of  motion  separate  from  each  other,  while 
everywhere   else   they  are   mingled   together.     But 
where  they  are  thus  mingled,  they  are  just  as  sepa- 
rate in  their  office  as  where  they  are   in   separate 
nerves. 

12.  Here,  in  Fig.   36,  is  a   representation  of  the 
brain  and  spinal  marrow,  with  the  nerves  branching 
out  from  them  in  all  directions.    At  a  is  the  cerebrum, 
the  upper  large  brain  filling  up  a  large  part  of  the 
skull,  and  at  Z>  is  the  cerebellum,  the  smaller  brain 
lying  underneath  the  cerebrum.     You  see  the  spinal 
marrow  extending  from  the  brain  down  the  back.    It 
is   very   much  like  the  brain  in  its  structure,    and 
should  really  be  considered  as  an  extension  of  the 
brain  itself.     You  see  that  nerves  branch  out  from 
the  brain  and  the  spinal  marrow  all  over  the  body. 

13.  You  observe  that  the  whole  of  this  nervous 
system  has  two  exactly  similar  halves,  just  as  it  is 
with  the  system  of  bones,  and  the  system  of  muscles. 
The  cerebrum  has  two  parts  just  alike,    called  the 
two  hemispheres  of  the  brain.     So  it  is  with  the  cere- 
bellum.    There  are  two  sets  of  nerves  also  for  each 
half  of  the  body  that  are  just  alike. 

In  what  parts  of  the  body  are  these  tubes  mingled  together  in  the 
same  nerves?  Where  are  they  in  separate  nerves?  Describe  the 
arrangement  of  the  nervous  system  represented  in  Fig.  36.  Is  the 
nervous  system  single  ?  What  are  the  hemispheres  of  the  brain  ? 


THE   NERVOUS    SYSTEM, 


99 


FIG.  36. 


100 


FIRST   BOOK    IN    PHYSIOLOGY. 


14.  In  Fig.  37,  you  see  the  general  arrangement  of 
the  brain.  It  is  a  view  of  one  of  the  halves  or  hem- 
ispheres of  the  brain.  It  is  the  inside  of  the  hemis- 
phere that  you  see.  At  a  l>  and  c  is  the  cerebrum  ; 
at/ is  represented  the  white  substance  that  joins  this 
hemisphere  to  the  other;  at  d  is  the  cerebellum, 


showing  a  very  beautiful  arrangement,  called  the 
arbor  vitce,  or  tree  of  life  ;  at  e  is  the  beginning  of  the 
spinal  marrow  ;  at  g  is  the  beginning  of  the  nerve  of 
sight,  and  at  I  is  the  nerve  of  smell.  Then  there  are 
various  other  nerves,  which  go  to  the  eye  and  other 
parts  of  the  face. 


37. 


Describe  the  representation  of  the  brain  and  its  nerves,  given  in  Fig. 


THE    NERVOUS   SYSTEM. 


101 


15.  Yon  observe  that  the  surface  of  tne' brain  'is 
very  irregular.  The  brain  does  not  touch  the  inside 
of  the  skull,  but  it  is  covered  by  three  different  mem- 
branes, one  of  which  is  very  strong  and^  thick,  so  as  to 
protect  this  delicate  organ  from  injury. 

FIG.  38. 


16.  The  brain  is  soft,  something  like  blancmange. 
It  is  the  softest  organ  in  the  body.  It  is  composed  of 
two  kinds  of  substance.  These  are  quite  well  repre- 
sented in  Fig.  38.  Here  the  upper  half  of  the  brain 
is  cut  off,  and  you  see  the  upper  cut  surface  of  the 


What  is  said  of  the  surface  of  the  brain,  and  of  its  coverings? 
is  the  consistence  of  the  brain  ? 


What 


102  FITR&T    BOOK    IN   PHYSIOLOGY. 

lower  half.  The  outer  shaded  part  is  a  grayish  sub- 
stance. All  on  the  inside  of  this  is  a  white  substance. 
You  see  the  dividing  line  between  the  two  halves  or 
hemispheres.  In  the  middle  of  the  Figure  is  repre- 
sented a  substance  which  makes  a  connection  between 
the  hemispheres.  It  is  probably  by  means  of  this 
connection  that  the  two  halves  of  the  brain  act  toge- 
ther as  one  brain. 

17.  It  is  curious  to  observe  that  the  white  part  of 
the  brain  is  just  like  the  nerves.     It  is,  like  them, 
composed  of  very  fine  tubes.     It  is  indeed  a  great 
central  collection  of  the  beginnings  of  nerves  that 
branch  out  all  over  the  bo'dy. 

18.  The  outer  gray  part  of  the  brain  is,  on  the  other 
hand,  made  up  of  cells,  instead  of  tubes.     This  is  sup- 
posed to  be  the  working  part  of  the  brain.     The  mind 
acts  directly  upon  the  gray  part  when  it  moves  any 
of  the  body.     Thus,  when  you  will  to  have  your  hand 
move,  the  mind  does  something,  but  what  we  know 
not,  to  some  part  of  this  gray  substance.     Then  an 
impression  or  message  is  sent  through  those  tubes  in 
the  white  substance  which  are  connected  with  this 
part  of  the  gray  substance.     And  as  these  tubes  ex- 
tend from  the  brain  in  the  nerves  to  the  muscles  of  the 
hand,  the  hand  is  moved. 

19.  In  sensation  all  this  is  reversed.    The  impression 
travels  just  the  contrary  way.     It  goes  to  the  brain, 
and  not  from  it,  as  it  does  in  motion.     If  any  one 
touches  you,  the  impression  is  carried  by  the  nervous 

What  are  the  two  kinds  of  substance  in  the  braiu,  and  how  are  they 
arranged  ?  What  is  the  white  substance  ?  Of  what  is  the  gray  sub- 
stance composed  ?  What  is  supposed  in  regard  to  it?  What  happens 
in  motion,  and  what  in  sensation  ? 


THE   NERVOUS    SYSTEM.  103 

tubes  to  some  portion  of  the  brain.  The  gray  sub- 
stance at  this  part  of  the  brain  receives  the  impression 
from  the  tubes  in  the  white  substance,  and  so  the 
mind  feels  it. 

20.  You  observe  that  I  have  used  the  words  impres- 
sion and  message  in  speaking  of  the  communication 
of  the  mind,  by  the  nerves,  with  all  parts  of  the  body. 
I  use  them  because  they  are  the  best  words  that  I  can 
use  in  our  present  state  of  knowledge  on  this  subject. 
We  do  not  know  what  it  is  that  is  sent  along  the 
nerves.  We  only  know  that  something  passes  through 
these  tubes  whenever  the  mind^feels  anything,  or  ex- 
cites the  muscles  to  action.     And^  n$t  knowing  what 
it  is,  we  speak  of  it  as  a  message  or*4^mpression. 

21.  There  have  been  many  supposil^s  on  this  sub- 
ject.    Some  have  supposed  that   electricity  travels 
along  the  nerves  just  as  it  does  along  the  wjres  of  a 
telegraph.     They  suppose  that  it  goes  from -the  brain 
when  the  mind  excites  the  muscles  to  action,  and  that 
it  goes  towards  the  brain  when  we  feel  any  sensation. 
Others  have  supposed  that  there  was  a  vibration  or 
shaking  of  the  substance  in  the  tubes  of  the  nerves 
from  one  end  of  them  to  the  other.     But  these  are 
mere  suppositions,  and  there  is  no  proof  that  they  are 
true.     Whatever  it  is  that  passes  through  the  nerves, 
it  must  pass  through  each  of  the  multitude  of  little 
tubes  separately,  for,  as  you  remember,  each  tube  has 
no  communication  with  any  of  the  other  tubes  with 
which  it  is  bound  up. 

22.  Not  only  are  there  different  nerves  for  sensa- 

Do  we  know  what  is  sent  along  the  nerves  ?     What  has  been  sup- 
posed in  regard  to  it  ? 


104  FIRST   BOOK    IN    PHYSIOLOGY. 

tion  and  for  motion,  as  you  learned  in  §10  and  §11, 
but  there  are  also  different  nerves  for  different  kinds 
of'sensation.  Thus,  the  nerve  that  informs  the  mind 
of  a  tickling  or  a  pain  in  the  nose,  is  not  the  same 
nerve  that  informs  the  mind  of  the  odors  that  you 
smell.  The  snuff-taker  feels  the  tingling  of  the  snuff 
with  one  nerve,  and  smells  it  with  another.  So,  too, 
in  the  eye,  the  nerve  with  which  the  mind  feels  a 
pain  there  is  not  the  same  nerve  with  which  it  sees. 

23.  There  are  also  about  the  face  different  nerves 
for   different   kinds   of   motions.       Thus,   the   nerve 
through  which  the  lower  jaw  is  moved,  in  eating,  is 
not  the  same  nerve  by  which  the  mind  works  the 
muscles  of  the  jaw  in  laughing  and  in  speaking. 

24.  There  mfo  organ  that  has  so  many  different 
nerves  as  the  eye.     It  has  two  different  nerves  for 
sensation  and  four  for  its  various  motions.     Its  ma- 
chinery of  nerves  and  muscles  is  therefore  very  com- 
plicated. 

25.  All  parts  of  the  body  are  not  equally  supplied 
with  nerves.     Some  parts  are  very  scantily  supplied, 
and  therefore  have  but  little  feeling,  as  it  is  expressed. 
There  are  few  nerves  in  the  bones,  and  so  when  a 
limb  is  cut  off,  the  sawing  of  the  bone  occasions  no 
pain.     There  is  not  much  feeling  in  the  muscles,  for 
although  they  are  well  supplied  with  nerves,  the  tubes 
in  these  nerves  are  the  tubes  for  motion  mostly,  and 
few  of  them  are  for  sensation.      The  skin  has  a  full 


What  is  said  in  §  22  of  the  different  kinds  of  nerves  ?  "What  is  said 
of  the  nerves  of  motion  in  the  face  ?  What  organ  has  more  nerves  than 
any  other  ?  What  is  said  of  different  parts  of  the  body  in  regard  to 
their  supply  of  nerves •? 


THE   NERVOUS   SYSTEM.  105 

supply  of  the  nerves  of  sensation.  In  cutting  off  a 
limb,  therefore,  the  chief  suffering  is  in  dividing  the 
skin. 

26.  The  skin  is  fully  supplied  with  nerves  for  two 
purposes  :  1,  that  it  may  act  as  the  organ  of  the  sense 
of  touch,  and  2,  that  it  may  warn  of  danger.     It  is, 
as  I  have  said  in  another  place,  a  sentinel  to  guard 
the  organs  inside  against  injury.     It  feels  the  least 
touch.     Its  nerves  at  once  send  their  warning  of  dan- 
ger to  the  mind,  and  the  mind  sends  its  orders  for 
action  to  the  muscles,  so  that  the  danger  may  be  re- 
treated from.     And  as  the  skin  stands  guard  so  faith- 
fully, there  is  no  need  that  the  muscles  and  bones  and 
other  internal  parts  should  be  very  sensitive. 

27.  There  is  one  office  of  the  nerves  that  I  have  not 
mentioned.     The  different  organs  of  the  body  sympa- 
thize "with  each  other,  and  it  is  through  the  nerves 
that  they  do  this.     Thus,  when  you  have  a  headache 
from  a  disordered  stomach,  it  is  because  the  brain 
sympathizes  with  the  stomach.     When  tears  flow  in 
grief,  it  is  because  the  tear-glands  are  excited  to  un- 
usual action  through  the  nerves.     The  sympathy  in 
this  case  is  with  the  brain.     The  sorrowful  mind,  by 
its  thoughts,  affects  the  brain.     Then  the  tear-glands, 
by  means  of  the  nerves  which  go  from  the  brain  to 
them,  sympathize  with  it,  and  so  they  make  and  pour 
forth  a  flood  of  tears. 

28.  There  are  many  actions  in  the  body  that  result 
from  the  connection  of  different  parts  by  the  nerves. 

For  what  two  purposes  is  the  skin  fully  supplied  with  nerves  ?  "Why 
is  there  no  need  that  the  muscles  and  bones  should  be  very  sensitive  ? 
By  what  is  the  sympathy  of  the  different  organs  of  the  body,  maintained  ? 


106  FIRST    BOOK    IN    PHYSIOLOGY. 

Thus,  when  there  is  something  in  some  of  the  pipes 
of  the  lungs,  causing  an  irritation  there,  we  cough  in 
order  to  throw  it  off  through  the  windpipe.  But  the 
muscles  that  perform  the  coughing  motion  are  not  in 
the  pipes.  They  are  outside  of  the  lungs  in  the  frame- 
work of  the  chest,  and  remove  the  irritating  substance 
by  forcing  the  air  out  against  it.  JSTow  the  reason 
that  these  muscles  are  excited  to  this  action  is  that 
they  are  connected  by  nerves  with  the  pipes  where 
the  irritation  is  felt.  So  it  is  in  sneezing.  If  some- 
thing irritate  the  lining  membrane  of  the  nose,  the 
muscles  of  the  chest  throw  the  air  from  the  lungs  with 
great  force  up  through  the  nose  to  expel  the  offending 
substance.  They  could  not  act  in  this  way  if  they 
were  not  connected  by  nerves  with  the  lining  mem- 
brane of  the  nostrils.  A  message,  as  we  may  say,  is 
sent  from  the  irritated  spot  down  to  the  muscles  of 
the  chest  through  the  nerves,  telling  them  to  send  up 
a  blast  of  air  to  expel  the  intruder. 

29.  From  what  I  have  told  you  in  this  chapter  in 
regard  to  the  nerves,  you  can  see  that  the  nervous 
system  is  a  very  complicated  system.  I  have  spoken 
only  of  those  things  in  it  which  you  can  easily  under- 
stand. In  my  larger  work  on  Physiology  I  go  into 
this  subject  much  more  extensively,  and  what  you 
have  learned  in  this  book  will  prepare  you  to  under- 
stand fully  what  is  contained  in  that. 

Upon  what  do  many  actions  in  the  body  depend  ?  Illustrate  by  the 
acts  of  coughing  and  sneezing. 


Jd#   w   '  ' 

• 


THE   BONES.  107 


CHAPTER   VIII. 
THE  BONES. 

1.  THE  bones  of  the  body  serve  many  different  pur- 
poses.    The  three  principal  of  these  I  will  notice.     1. 
They  form  the  solid  framework  of  the  body.     In  this 
respect  they  are  to  the  body  what  timbers  are  to  a 
building.     2.  Some  of  the  principal  bones  also  form 
cavities  in  which  important  organs  are  securely  in- 
closed.    Thus,  the  soft  delicate  brain  is  made  very 
secure  by  being  inclosed  in  that  round  box  of  bones 
called  the  skull  or  cranium.     So,  also,  the  lungs  and 
the  heart,  as  you  saw  in  the  chapter  on  Respiration, 
are  very  carefully  shut  up  in  a  barrel-shaped  frame 
of  banes,  united  firmly  by  ligaments  and  muscles.     3. 
The  bones  serve  another  important  purpose  in  being 
moved  by  muscles.      When  they  move  upon  each 
other  at  the  joints  it  is  the  muscles  that  make  them 
move.     The  bones  are,  therefore,  a  part  of  the  ma- 
chinery that  the  mind  moves  by  means  of  the  ner- 
vous system.     This  use  of  the  bones  shows  you  why  I 
introduce  this  subject  here. 

I  have  told  you  in  Chapter  II,  §3,  of  what  two 
substances  the  bones  are  composed,  and  shall,  there- 
fore, say  nothing  here  on  that  subject. 

2.  The  bones  in  our  bodies  are  covered  up  from 
view  by  the  ligaments,  muscles,  tendons,  and  the  skin. 
But  this  is  not  so  with  the  skeletons  of  all  animals. 
Some  have  their  skeletons  on  the  outside  of  the  body. 

What  are  the  three  principal  purposes  that  the  bones  answer  ?  Of 
what  two  kinds  of  substance  are  the  bones  composed? 


108  FIRST   BOOK    IN    PHYSIOLOGY. 

This  is  the  case,  for  example,  with  turtles,  crabs  and 
lobsters.  With  them  the  skeleton  is  a  coat  of  mail  to 
defend  the  soft  parts  from  injury. 

3.  The  bones,  although   they  are  so   hard,  grow 
together  with  all  the  soft  parts  that  surround  them. 
Thus,  when  the  arm  of  a  child  grows  to  be  the  stout 
arm  of  a  man,  the  bones  enlarge  equally  with  the 
muscles,   tendons,  &c.     They  enlarge,  just  as  these 
other  parts  do,  from  particles  added  by  the  formative 
vessels  from  the  blood ;  for,  although  they  are    so 
hard,  the  blood  circulates  in  them. 

4.  The  teeth,  which  are  so  much  like  the  bones, 
differ  from  them  in  regard  to  growth.     When  a  tooth 
first  shoots  up  out  of  the  gum,  its  body  is  as  large  as 
it  ever  will  be.     It  cannot  grow  larger,  as  the  bones 
do,  because  the  hard  enamel  can  have  no  circulation 
in  it.     If  the  teeth  could  grow  larger  there  would  be 
no  need  of  having  a  second  set  to  take  the  place  of 
the  first.     There  would  then  need  to  be  simply  an 
addition  of  more  teeth  as  the  jaw   enlarged.    But  as 
it  is  now,  all  the  first  set  are  removed,  because  they 
would  be  too  small  for  the  large  jaw  of  the  adult,  and 
thirty-two  large  teeth  take  the  place  of  the  twenty 
small  ones  of  the  first  set. 

5.  The  bones  are  not  perfectly  solid.     They  would 
be  too  heavy  if  they  were  so.     Some  parts  of  them 
are  made  up  of  cells,  as  the  large  ends  of  the  long 
bones.     The  shafts  of  these  bones  are  hollow.     This 
is  for  the  purpose  of   making  them  strong,  and  at 

By  what  are  the  bones  in  our  bodies  covered  ?  Are  they  covered  up 
in  all  animals?  "What  is  said  of  the  growth  of  bones?  How  do  teeth 
differ  from  bones  ?  Why  are  there  two  sets  of  teeth  ? 


THE   BONES 


109 


FIG.  39. 


the  same  time  light.  In  Fig. 
39  you  see  the  thigh-bone  and 
the  bone  of  the  arm.  In  both 
the  shaft  is  hollow,  while  the  large 
ends  are  chiefly  made  up  of  cells. 
In  birds  it  is  very  necessary  that 
the  bones  should  be  light  while 
they  are  strong,  so  that  they  may 
not  be  burdensome  in  flying.  In 
them,  therefore,  the  bones  are 
very  hollow.  They  are  so  for  the 
same  reason  that  the  stalks  of  tall 
grass  and  of  grain  are  hollow.  If 
these  were  solid,  and  therefore 
more  slender,  they  would  break 
very  easily  as  the  wind  bent  them 
over.-  And  in  constructing  build- 
ings, the  architect  very  well 
knows  that  a  hollow  pillar  has 
more  strength  than  the  same 
quantity  of  wood  in  a  solid  form. 

6.  The  bones  have  a  great  variety  of  shapes  accord- 
ing to  their  different  uses.  You  see  this  to  be  true  as 
you  look  at  the  skeleton  in  Fig.  40.  In  the  skull, 
which  holds  the  brain,  you  see  the  bones  so  shaped 
and  arranged  as  to  form  a  somewhat  round  box.  At 
the  under  part  of  this  box  in  front  are  bones  of  various 
shapes  to  accommodate  the-  organs  of  four  of  the 


Why  are  the  bones  not  solid  ?  How  are  the  long  bones  at  their  end»? 
"Why  are  the  shafts  of  these  bones  hollow  ?  Why  are  they  very  hollow 
in  birds  ?  What  is  said  of  the  stalks  of  plants  and  the  pillars  of  build 
ings? 


110  FIRST   BOOK   IN    PHYSIOLOGY, 

FIG.  40. 


THE   BONES. 


Ill 


senses,  seeing,  bearing,  tasting  and  smelling.  Then 
there  is  the  bone  of  the  lower  jaw,  shaped  something 
like  a  horse-shoe.  The  bones  of  the  chest  form  a  bar- 
rel-shaped cavity  for  the  heart  and  lungs.  The  spinal 
column,  Jc,  made  up  of  twenty-four  bones,  extends  the 
whole  length  of  the  body  as  its  main  pillar.  To  this 
are  fastened  the  slender  ribs  which  are  joined  to  the 
flat  breast-bone  in  front  by  means  of  cartilages.  The 
spinal  column,  you  observe,  stands  firmly  supported 
upon  a  thick  bone  which  is  .wedged  in  between  two 
broad  flaring  bones,  I  and  m.  This  bcfwl-form  collec- 
tion of  bones,  called  the  pelvis,  supports  the  contents 
of  the  abdomen.  You  observe  the  large  bones  of  the 
thigh  and  leg,  which  are  made  for  firmness,  and  the 
lighter  bones  of  the  upper  extremity,  which  are  fitted 
for  quickness  and  variety  of  motion.  I  will  now  no- 
tice some  of  the  bones  more  particularly. 

7.  In  Fig.  41  you  see  the  bones  of  the  head — that 
is,  all  of  them  that  are  in 
sight  in  front.  There  are 
twenty-two  bones  in  the  head, 
but  some  of  them  are  out  of 
sight.  Fourteen  of  these  be- 
long to  the  face.  Eight  be- 
long to  the  cranium,  that  is, 
the  part  of  the  skull  that 
holds  the  brain.  Of  these 
observe  particularly  the  large 
bone  of  the  forehead,  a, 
called  the  frontal  bone,  the 


FIG.  41. 


What  is  said  of  the  shapes  of  bones  ?  Describe  the  skeleton  as  rep- 
resented in  Fig.  40.  How  many  bones  are  there  in  the  head  ?  How 
many  of  them  belong  to  the  cranium  ?  Describe  these  as  seen  in  Fig.  41. 


112  FIRST   BOOK   IN    PHYSIOLOGY. 

parietal  bone,  5,  and  the  temporal  bone,  or  bone  of  the 
temples,  c.  There  is  a  bone  in  the  rear,  forming  the 
back  of  the  cranium,  as  the  frontal  bone  forms  the 
front.  These  bones,  with  two  others  on  the  under 
part  of  the  cranium,  make  the  round  box  that  holds 
the  brain. 

8.  The  cranium  is  made  round  because  it  will  not 
break  as  easily  as  it  would  if  it  were  of  some  other  • 
shape.     This  is  one  reason  also  why  it  is  made  up  of 
so  many  different  bones,  instead  of  being  one  solid, 
tight  box.     If  a  blow  be  received  on  the  head,  these 
bones  give  a  little  upon  each  other,  as  it  is  expressed, 
and  so  they  are  not  often  broken.     They  give  more 
in  the  child  than  in  the  adult,  because,  besides  being 
less  brittle,  they  are  less  tightly  put  together.     It  is 
well  that  it  is  so ;  for  if  it  were  not,  the  skull  would 
often  be  fractured,  in  the  frequent  falls  which  the 
child  has. 

9.  The  bones  on  the  top  of  the  head  are  fastened 
together  by  what  are  called  sutures.    They  are  locked 
together  by  little  teeth  of  bone,  which  shoot  by  each 
other,  as  you  see  in  Fig.  42.     Here  ~b  is  the  suture 
across  the  top  of  the  head  between  the  two  parietal 
bones  :  a  a  is  that  between  the  two  parietal  bones  and 
the  frontal  bone  in  front ;  and  c  c  is  that  between  the 
parietal  bones  and  the  bone  at  the  back  part  of  the 
cranium.     In   the    young   child    these    joinings   by 
suture  are  not  formed,  and  in  the  infant  the  bones  are 
quite  apart  in  some  places,  especially  at  the  upper  part 
of  the  forehead,  as  you  can  perceive  by  the  touch. 

Why  is  the  cranium  round  ?  Why  is  it  made  of  so  many  bones  ? 
What  are  the  sutures  of  the  skull  ?  What  is  said  of  the  joinings  of  the 
bones  of  the  skull  in  the  child  ? 


THE    BONES.  113 


FIG.  42. 


10.  The  bones  of  the  cranium,  together  with  their 
coverings,  are  well  fitted  to  guard  the  delicate  brain 
from  injury  by  the  blows  to  which  the  head  is  so 
much  exposed.     When  a  blow  is  received,  its  force  is 
broken  by  the  hair,  the  skin,  and  the  muscles,  that 
extend  over  the  bones.     And  then  the  bones  them- 
selves, as  I  have  before  said,  give  a  little  upon  each 
other.     It   requires   therefore   a  very  hard  blow  to 
break  the  skull. 

11.  The  spinal  column  is  the  most  wonderful  part 
of  the  bony  machinery  of  the  body,  because  it  serves 
so  many  different  purposes.     It  is  the  great  pillar  of 
the  body,  and  yet  it  is  a  chain  of  twenty-four  bones, 
that  can  be  bent   considerably,  especially  in   some 
parts  of  it.     And"  besides,  there  is  a  canal  moving 
through  all  this  chain  of  bones,  in  which  lies  securely 
the  spinal  marrow,  an  organ  as  delicate  and  as  essen- 

Hcw  is  the  delicate  brain  guarded  against  injury  ?     Mention  the  sev- 
eral uses  of  the  spinal  column  ?     Of  how  many  vertebrae  is  it  composed  I 


114  FIRST    BOOK   IN    PHYSIOLOGY. 

tial  to  life  as  the  brain  itself.  Then  there  are  nerves 
branching  out  from  the  spinal  marrow,  between  the 
twenty-four  bones,  in  such  a  way  that  they  are  never 
pressed  upon. 


12.  The  twenty-four  bones  of  the  spinal  column  are 
called  vertebra,  (plural  of  vertebra.)  In  Fig.  43,  you 
see  one  of  these  vertebrae ;  a  being  the  body  of  the  bone; 
£  the  hole  through  the  vertebra  which  forms  its  part 
of  the  canal  for  the  spinal  marrow  ;  and  c  the  spinous 
process,  as  it  is  called.  The  hard  ridge  that  you  feel 
in  passing  your  finger  up  and  down  the  middle  of  the 
back,  is  the  row  of  these  spinous  processes.  Each  ver- 
tebra has  six  other  processes,  only  two  of  which  you 
can  see  in  the  figure.  The  bones  of  the  whole  column 
are  so  locked  together  by  these  processes,  that  they 
cannot  be  separated  from  each  other  or  dislocated 
without  being  broken.  In  Fig.  44  you  have  a  side 
view  of  the  same  vertebra.  As  you  look  at  the  spinal 

Describe  the  vertebrae  as  represented  in  Figs.  43  and  44.  How  many 
processes  or  projections  has  each  vertebra  ?  What  is  the  use  of  them  ? 
By  what  are  they  covered  ? 


THE   BONES. 


column  in  front,  it  is  a  round  smooth  column ;  but  in 
the  rear  the  processes  make  it  very  jagged.  These 
are  all^however,  covered  up  by  muscles,  except  the 
row  of  spinous  processes. 

13.  In  Fig.  45,  you  see  the  whole  col- 
umn,  with  the  stout  bone  on  which  it 
stands.  It  is  represented  as  sawn  down 
through  its  whole  length,  so  that  you  see 
but  half  of  it.  You  see  the  bodies  of  the 
vertebrae  in  front,  and  the  spinous  pro- 
cesses on  the  other  side.  Between  the  row 
of  the  bodies  of  the  vertebrae  and  the  row 
of  spinous  processes  you  see  the  canal  in 
which  lies  the  spinal  marrow.  You  ob- 
serve that  there  are  spaces  between  the 
bodies  of  the  vertebrae.  These  spaces 
are  filled  with  pieces  of  cartilage  or 
gristle.  If  it  were  not  for  these  carti- 
lages you  could  not  bend  the  back-bone 
forward  at  all,  but  could  only  bend  your 
body  on  the  heads  of  the  thigh-bones, 
with  a  hinge-like  motion,  which  would 
be  very  stiff  and  awkward.  As  it  is, 
when  you  bend  forward,  in  addition  to 
this  hinge-like  motion,  the  bodies  of  all; 
the  vertebrae  come  nearer  together.  In 
doing  so  the  cartilages  between  them  are 
compressed,  and  so  are  made  smaller. 
And  as  you  straighten  up  again,  these 
cartilages,  by  their  elasticity,  return  to  their  usual 

Describe  the  spinal  column  as  represented  in  Fig.  45.     Of  what  use 
are  the  cartilages  ? 


116  FIRST   BOOK   IN    PHYSIOLOGY. 

size  again.  From  the  constant  pressure  on  these  car- 
tilages, as  you  go  about  during  the  day,  you  are  not 
quite  as  tall  at  night  as  you  are  in  the  morning.  So 
also  in  old  age,  one  becomes  less  tall  than  in  the  vigor 
of  manhood,  because  these  cartilages  shrink. 

14.  The  spinal  column  can  be  bent  not  only  for- 
wards, but  in  other  directions  also — to  either  side  and 
backwards.     This  chain  of  bones  can  also  be  some- 
what twisted,  as  we  may  express  it,  as  you  turn  your 
body  one  way  and  another.     As  you  do  this,  each 
bone  moves  with  a  rotary  motion  a  very  little.     But 
as  there  are  twenty-four  bones,  all  these  little  motions 
between  them  together  make  a  considerable  twist  of 
the  whole  column.     Now,   as  there   is  through  the 
whole  length  of  this  column  a  rod  of  very  delicate 
substance  that  must  not  be  pressed  upon,  all  these 
motions  have  to  be  most  carefully  arranged.     The 
bones  must  be  nicely  fitted  with  all  their  processes ; 
they  must  be  well  fastened  together  with  ligaments ; 
and  then  the  muscles  that  move  all  these  twenty-four 
bones  must  all  of  them  work  exactly  aright.    All  this 
is  done,  and  the  back-bone,  as  we  call  it,  is  a  set  of 
machinery  vastly  more  complicated  and  more  nicely 
arranged  than   any  machinery  that  man  ever   con- 
trived. 

15.  But  the  most  wonderful  part  of  this  machinery 
is  at  the  top  of  the  column.     There  the  motions  are 
more  free  than  in  any  other  part  of  the  column,  as 
you  see  when  you  bow  your  head,  and  bend  and  turn 

In  what  part  of  the  day  are  you  the  tallest  ?  What  is  said  of  the 
various  motions  of  the  spine  ?  What  is  said  of  it  as  a  piece  of  machine- 
ry ?  What  is  the  most  wonderful  part  of  this  machinery  ? 


THE   BONES.  117. 


it  in  various  directions.  There  are  two  different  mo- 
tions made  by  the  head  on  the  top  of  the  column. 
The  first  of"  these  is  when  you  move  the  head  back- 
ward and  forward.  In  doing  this  it  rocks  on  the  first 
vertebra,  the  topmost  bone  of  the  spinal  column. 
For  this  purpose  there  are  two  smooth  rounded  sur- 
faces, that  work  in  two  smooth,  hollow  places  in  the 
vertebra. 

16.  The  other  motion  is  when  you  turn  your  head 
to  look  at  the  one  side  or  the  other.     In  performing 
this  rotary  motion  the  skull  does  not  move  alone,  as 
in  the  first  motion,  but  it  moves  together  with  the 
first   vertebra.      The   first   vertebra  in   this   motion 
moves  on  the  second  around  a  tooth-like  process  that 
stands  up  from   this  second   vertebra.      This   tooth 
works  in  a  smooth  notch  on  the  inside  of  the  first  ver- 
tebra.    It  is  bound  very  fast  in  this  notch  by  a  strong 
ligament,  so  that  it  may  not,  in  any  of  the  quick  mo- 
tions of  the  head,  be  made  to  press  FIG.  45. 

on  the  delicate  spinal  marrow  which 
lies  against  it.  In  Fig.  46  you  see 
these  two  vertebrae,  and  notice  the 
tooth-like  process  of  the  second 
standing  up  on  the  inside  of  the 
first  vertebra. 

17.  You  see,  then,  that  when  you  move  your  head 
backward  and  forward,  you  move  it  in  a  hinge-like 
way  on  the  first  bone  of  the  spine ;  and  when  you 
turn  the  head  to  look  to  the  right  or  the  left,  you 


How  many  motions  are  performed  by  the  head  on  the  top  of  the 
spinal  column  ?  Describe  the  manner  in  which  the  first  of  these  motions 
is  performed.  Then  the  second. 


118  FIRST    BOOK    IN    PHYSIOLOGY. 

turn  the  head  and  this  first  bone  together  as  one 
thing  on  the  tooth-like  process  of  the  second  bone. 
There  is  an  arrangement  somewhat  like  this  in  the 
standard  of  telescopes.  There  is  first  a  hinge-joint, 
as  in  the  case  of  the  head,  so  that  you  can  move  'the 
telescope  up  and  down  so  as  to  look  as  high  or  as  low 
as  you  wish.  There  is,  also,  in  the  standard  another 
joint,  with  a  rotary  motion,  by  which  you  can  turn 
the  telescope  so  as  to  see  as  far  to  the  one  side  or  to 
the  other  as  you  please.  This  is  like  the  motion  per- 
formed between  the  first  and  second  vertebra. 

18.  The  vertebrae  vary  much  in  different  kinds  of 
animals.  Here,  for  example,  in  Fig.  47,  is  the  verte- 
bra of  a  fish,  which  you  see  differs  very  much  from 
the  vertebrae  of  man,  as  represented  in  Figs.  43  and 
44.  It  has  but  two  processes,  ff.  In  man  there  is  a 
iiG.47.  single  short  spinous  process  behind,  wiiile 
the  vertebra  is  round  in  front.  But  in  the 
fish  there  are  two  quite  long  spinous  pro- 
cesses, one  in  front  and  the  other  in  the 
rear  ;  or  rather,  we  should  say,  according 
to  the  common  position  of  the  fish  in  the 
water,  one  above  and  the  other  below. 
There  is  a  curious  contrivance  in  the  ar- 
rangement of  the  vertebrse  of  the  fish  for 
making  the  spine  flexible.  Each  vertebra  has  a  cup- 
like  cavity  on  each  side  towards  the  next  vertebra. 
Each  two  vertebrse  then  put  together  make  a  cavity 
of  this  £\  shape.  This  cavity  is  lined  with  a 


Give  the  comparison  between  this  arrangement  and  that  of  a  stand- 
ard of  a  telescope.  Describe  the  vertebrse  of  a  fish  and  their  arrange- 
ment. 


THE   BONES.  H9 


membrane  making  a  sac,  and  in  this  is  a  fluid  some- 
thing like  the  white  of  an  egg.  These  sacs,  thus 
filled  with  fluid,  make  soft  cushions  between  all  the 
bones  of  the  spine,  upon  which  the  bones  rock  in  the 
various  motions  of  the  fish.  This  arrangement  you 
can  observe  for  yourself  whenever  you  have  fish  on 
the  table. 

19.  In   snakes  the  spinal   column   is   exceedingly 
flexible.     It  is  made  so  in  two  ways.     First,  there  is 
a  great  number  of  vertebrae.     The  result  of  this  is, 
that  in  a  very  extensive  motion  of  the  whole  spine 
the  motion  between  each  two  vertebras  is  very  little. 
The  motion  is  divided  up,  as  we  say.     The  rattlesnake 
has  over  two  hundred  vertebras,  and  the  great  boa- 
constrictor  has  three  hundred  and  four.     Secondly, 
the  flexibility  of  the  spine  of  these  animals  is  secured 
by  having  a  ball  and  socket  joint  between  all  the  ver- 
tebras.    A  smooth  round  ball  in  each  vertebra  works 
in  an  equally  smooth  cup-like  hole  in  the  one  next  to  it. 

20.  The  framework  of  the  chest  I  have  described  to 
you  in  the  chapter  on  Kespiration  §  10.     There  are 
two  bones  outside  of  this  barrel-shaped  framework 
that  I  will  now  notice.     First,  there  is  the  collar-bone 
<7,  Fig.  40.     This  is  fastened  to  the  breast-bone  at  one 
end,  and  at  the  other  end  is  fastened  to  a  process  'of 
the  shoulder-blade,  and  helps  to  make  the  top  of  the 
shoulder.     It  is  a  sort  of  prop  or  brace,  that  keeps  the 
shoulder  braced  out  in  its  place. 


By  what  two  means  are  the  spinal  columns  of  snakes  made  so  flexi- 
ble ?  How  many  vertebrae  has  the  rattle-snake  ?  •  How  many  has  the 
boa-constrictor  ?  What  is  the  use  of  the  collar-bone,  and  how  is  it 
placed  ? 


120  FIRST   BOOK    IN   PHYSIOLOGY. 

21.  The  shoulder-blade  is  a  very  singular  bone.   Its 
back  part,  that  which  is  towards  the  spine,  is  quite 
thin,  and  is  covered  on  both  sides  with  muscles  that 
move  it.     It  is  designed  to  give  freedom  to  the  mo- 
tions of  the  arm.     "When  you  draw  your  arm  back 
very  much,  you  can  see  that  there  is  considerable  mo- 
tion of  the  shoulder-blade.     This  is  because  the  mus- 
cles that  are  attached  to  it  pull  it  back,  at  the  same 
time  that  other  muscles  pull  the  arm  in  the  same 
direction.     And  as  the  shoulder-blade  forms  at   its 
upper  part  the  shoulder-joint,  these  muscles  in  pulling 
back  the  bone  pull  back  the  whole  joint,  and  of  course 
the  arm  with  it.     You  can  see  that  the  arm  could  not 
be  drawn  so  far  back  if  the  shoulder-joint  were  made 
without  any  shoulder-blade.      It  could  have  been  so 
made,  but  it  would  have  been  awkward  and  stiff  in 
its  motions. 

22.  Where  the  shoulder-blade  forms  the  shoulder- 
joint  there  is  a  shallow  cup-like  surface,  lined  with 
cartilage,  which  is  as  smooth  as  the  finest  polished 
ivory.     The  bone  of  the  arm  which  fits  into  it  has  its 
end  in   the  form  of  a  ball,  which  is  also  tipped  with 
cartilage  as  smooth  as  that  in  the  cup.     Observe  what 
keeps  this  ball  in  the  cup  as  it  moves  about  in  it. 
There  is  a  thick  skin  attached  all  around  the  edge  of 
the  cup  and  fastened  down  over  the  ball.     Besides 
this  stout  ligament,  there  is  another  remarkable  con- 
trivance for  keeping  the  round  head  of  the  bone  in  its 
place.      The  tendon  of  a  large   muscle  works  in  a 

Describe  the  arrangement  of  the  shoulder-blade.  How  does  it  make 
the  motions  of  the  arm  free  ?  Describe  the  shoulder-joint.  In  what  two 
ways  ia  the  joint  guarded  against  dislocation? 


THE   BONES.  121 


groove  on  the  front  of  this  head  of  the  bone,  and  thus 
holds  it  so  as  to  keep  it  from  slipping  out  of  the  cup. 

23.  It  is  Necessary  that  the  joint  should  be  thus 
carefully  guarded,  because  the  cup  or  socket  is  so 
shallow.  As  it  is,  although  it  is  so  well  guarded,  it  is 
very  often  dislocated.  It  might  have  been  made 
more  secure  by  having  the  socket  deeper ;  but  then 
the  motions  of  the  arm  could  not  be  as  free  as  they 
are  now,  and  freedom  of  motion  you  can  readily  see 
is  very  important  in  this  part  of  the  machinery  of  the 
body. 

24:.  The  arm-bone,  i,  Fig.  40,  is  jointed  at  the 
elbow,  with  the  two  bones  of  the  fore-arm  (so  called) 
and  seen  at  o  and  n.  The  elbow-joint  is  different  alto- 
gether from  the  joint  at  the  shoulder,  for  the  motion 
is  in  one  direction  only,  back  and  forth  like  a  hinge. 
It  is  therefore  called  a  hinge-joint,  while  that  at  the 
shoulder  is  called  a  ball-and-socket-joint.  In  whirling 
a  skipping-rope,  you  use  the  joint  at  the  shoulder;  but 
in  striking  with  a  hammer,  you  use  the  hinge-joint  at 
the  elbow. 

25.  The  hand  moves  on  the  fore-arm  at  the  wrist 
with  a  hinge-joint.  The  fingers  have  hinge-joints, 
except  where  they  are  joined  to  the  hand.  There 
they  have,  besides  the  hinge-like  motion,  something 
of  the  motion  of  a  ball-and-socket-joint.  The  motions 
of  the  thumb  are,  as  you  see,  quite  different  in  some 
respects  from  those  of  the  fingers. 


Why  is  this  joint  so  carefully  guarded  ?     How  could  it  have  been 
made  more  secure?      Why  was  it  not?      Describe   the   elbow-joint. 
How  does  it  differ  from  the  shoulder-joint  ?     Describe  the  joints  of  the 
wrist  aud  fingers  and  thumb. 
6 


122 


FIRST    BOOK    IN    PHYSIOLOGY. 


26.  Besides  these  mo- 
tions that  I  have  descri- 
bed, there  is  a  rotat^y 
motion  of  the  arm,  as 
you  turn  the  palm  of 
the  hand  up  and  down. 
This  is  done  by  a  pecu- 
liar motion  of  the  two 
bones  of  the  fore-arm. 
I  will  make  this  clear  to 
you  by  Fig.  48.  You 
see  that  the  largest  end 
of  the  ulna,  a,  is  at  the 
elbow,  while  the  largest 
end  of  the  radius,  5,  is 
at  the  wrist.  Now,  the 
hinge-like  motion  at  the 
wrist  is  performed  whol- 
ly with  the  large  end  of 
the  radius.  The  small 
end  of  the  ulna,  marked 
#,  has  nothing  to  do  with 
it,  but  is  loose,  and  has  a  rolling  motion  on  the  end  of 
the  radius.  It  is  just  the  reverse  with  these  two  bones 
at  the  elbow-joint.  The  hinge-motion  there  is  per- 
formed with  the  large  end  of  the  ulna,  a,  and  the  small 
end  of  the  radius,  ~b  has  nothing  to  do  with  it,  but  rolls 
on  the  end  of  the  ulna. 

27.  The  effect  of  this  arrangement  is  this.     When 
the  palm  of  the  hand  is  upward,  as  represented  in  the 


How  is  the  rotary  motion  of  the  fore-arm  made? 


THE    BONES.  123 


Figure,  these  two  bones  are,  as  you  see,  nearly  paral- 
lel. But  when  the  palm  is  turned  over,  they  are,  as 
we  may  say,  twisted  upon  each  other,  the  ulna,  #,  roll- 
ing on  5,  at  its  lower  end,  and  the  radius,  £,  rolling  on 
#,  at  its  upper  end.  You  can  see  these  two  positions 
of  these  bones  in  Fig.  40.  In  the  right  arm  you  see 
the  palm  of  the  hand  towards  you,  and  the  radius  and 
ulna  are  parallel.  In  the  left  arm  the  palm  is  partly 
turned  from  you,  and  these  bones  are  twisted  upon 
each  other  by  their  rolling  or  rotary  motion. 

28.  Observe  now  how  many  different  motions  there 
are  in  the  arm  and  hand.  *  They  are,  the  motion  of  the 
ball-and-socket-joint  at  the  shoulder,  the  hinge-motion 
at  the  elbow,  the  rolling  of  the  two  bones  at  the  fore- 
arm upon  each  other,  the  hinge-motion  at  the  wrist, 
the  hinge-motions  of  the  fingers  at  their  joinings  with 
the  hand,  together  with  something  of  a  ball-and-socket- 
motion,  the  hinge-motions  of  the  other  joints  of  the 
fingers,  and  the  free  motions  of  the  thumb  differing 
somewhat  from  those  of  the  fingers. 

29.  In  observing  these  motions  you  will  see  the  rea- 
son why  there  are  different  kinds  of  motion  in  differ- 
ent parts  of  this  complicated  machinery.     You  can 
see,  for  example,  why  there  is  a  hinge-motion  in  one 
place  and  that  of  a  ball-and-socket  joint  in  another, 
and  why  the  two  motions  are  united  in  the  joints 
which  the  fingers  make  with  the  hand,  while   the 
other  joints  of  the  fingers  can  perform  only  the  hinge- 
motion. 


Mention  the  different  motions  of  the  arm  and  hand  in  their  order,  be- 
ginning at  the  shoulder-joint.  What  is  said  of  the  two  kinds  of  motion, 
the  hinge-like  and  the  ball-and-socket-motion  ? 


124 


FIRST   BOOK    IN    PHYSIOLOGY. 


FlG- 49-  30.  You  see  that  there  are 

many  bones  in  the  hand — 
twenty -seven  in  all.  There 
are  eight  small  bones  called 
the  carpal  bones,  represented 
at  d,  in  Fig.  48.  These  are 
tightly  packed  together,  and 
lie  next  to  the  bones  of  the 
fore-arm.  The  metacarpal 
bones,  <?,  make  the  frame- 
work of  the  flat  part  of  the 
hand.  They  are  very  much 
like  the  first  row  of  the  bones 
of  the  fingers,/1.  But  they 
are  firmly  bound  together  by 
ligaments.  These  ligaments 
you  can  see  in  Fig.  49.  At 
d  d,  you  see  those  that  bind 
the  metacarpal  bones  together  at  their  beginning,  and  at 
e  e>  those  that  bind  them  at  their  ends,  where  the  bones 
of  the  fingers  are  jointed  with  them.  At  a,  £,  c,  and  </, 
are  other  ligaments  that  bind  the  carpal  bones  together. 
31.  You  notice  that  there  are  twelve  bones  in  the 
frame-work  of  the  hand,  aside  from  the  fingers — that  is, 
the  eight  carpal  and  the  four  metacarpal  bones.  The 
chief  reason  for  having  so  many  bones  thus  packed 
together  is  this.  Although  they  are  bound  together, 
there  is  some  little  motion  between  them,  and  this 
makes  the  hand  more  light  and  springy  than  it  would 
be  if  these  twelve  bones  were  all  in  one. 

How  many  bones  are  there  in  the  hand  \  Describe  their  arrangement. 
How  many  bones  are  there  in  the  framework  of  the  hand  1  Why  are 
there  so  many? 


THE    BONES. 


125 


32.  The  bones  of  the  lower  extremities  have  not  so 
much  freedom  of  motion  as  those  of  the  upper.     The 
chief  object  is  firmness,  as  they  support  the  weight  of 
the  body  in  moving  about.     They   are  larger  there- 
fore than  the  bones  of  the  upper  extremity,  as  you  see 
in  Fig.  40,  and  their  joints  are  much  more  stout  and 
secure. 

33.  In  Fig.  50,  you  have  a  rear 
view  of  the  thigh-bone.     Its  round 
head,  #,  fits  into  a  deep  socket  in 
the  pelvis,  as  represented  in  Fig. 
40.     Observe  the  reason  of  the  dif- 
ference in  regard  to  the  depth  of 
the  socket  between  this  joint  and 
the  shoulder-joint.    In  the  hip-joint 
strength  is  especially  needed ;  while 
freedom  of  motion  is  more  needed 
in  the  joint  of  the  shoulder,  and  so 
its  cup  or  socket  is  made  shallow. 
The  head  of  the  thigh-bone  is  held 
in  its  socket  by  the  same  kind  of 
ligament  that  I  have  described  in 
§  22,  as  securing  the  shoulder-joint. 
It  clasps  the  neck  of  the  bone,  <?, 
and  is  fastened  all  around  the  edge 
of  the  socket.     There   is   another 
ligament  also.    At  5  you  see  a  little 
hole,  in  which  one  end  of  this  liga- 
ment, which  is  short  and  stout,  is 
fastened.    The  other  end  is  attached 

What  is  said  of  the  difference  between  the  bones  of  the  upper  and 
the  lower  extremities  ?  Describe  the  thigh-bone.  Why  is  the  socket 
of  the  hip-joint  deeper  than  that  of  the  shoulder-joint  ?  Describe  the 
ligaments  of  the  hip  joint. 


f 


126  FIRST   BOOK    IN   PHYSIOLOGY. 

to  the  bottom  of  the  socket.  At  d  and  e  are  two  pro- 
jections, to  which  are  attached  large  muscles,  that 
move  the  thigh.  Along  the  whole  length  of  the  bone 
is  a  rough  ridge,  A,  for  fche  attachment  of  muscles.  At 
i  and  7c  are  two  smooth  surfaces,  which  form  with  the 
large  bone  of  the  leg,  the  hinge-joint  at  the  knee. 

34-.  There  is  a  small  thick  bone  fitting  over  the 
knee-joint  in  front,  called  the  knee-pan.  This  is  seen 
at  £,  in  Fig.  40.  One  of  its  uses  is  to  shield  the  joint. 
It  wards  off  blows,  and  prevents  the  joint  from  being 
injured  by  falls.  It  has  another  very  important  use, 
of  which  I  speak  particularly  in  my  larger  work  on 
Physiology. 

35.  The  leg  has  two  bones.  One  of  them,  u,  Fig. 
40,  is  very  large.  It  sustains  the  whole  weight  of  the 
body.  It  has  two  smooth  surfaces  at  the  knee/joint, 
on  which  work  the  two  smooth  surfaces  of  the  thigh- 
bone, i  and  #,  seen  in  Fig.  50.  The  other  bone  of  the 
leg,  v,  Fig.  40,  is  very  slender.  It  is  firmly  connected 
with  the  large  bone  by  ligaments  and  muscles.  The 
two  chief  uses  of  this  bone  are,  to  furnish  a  hold  for 
some  of  the  muscles,  and  to  make  the  outer  side  of 
the  ankle-joint.  The  inner  side  of  this  joint  is  made 
by  the  larger  bone.  This  joint  is  made  by  these  two 
bones  projecting  down  over  a  bone  in  the  foot  repre- 
sented at  /,  in  Fig.  51.  It  is  a  hinge-joint.  It  is 
made  quite  loose,  however,  so  that  the  foot  can  be 
turned  inward  and  outward.  And  yet  it  is  a  very 
firm  joint,  for  the  bones  of  the  leg  jut  over  strongly 
on  each  side,  and  the  ligaments  are  very  stout. 

"What  is  said  of  the  knee-pan  ?  Describe  the  bones  of  the  leg.  What 
are  the  uses  of  the  small  boue  of  the  leg  ?  What  is  said  of  the  ankle- 
joint  ? 


THE    BONES.  127 


36.  In  Fig.  51  are  represented  the  bones  of  the  foot. 
At  e  dfg  and  h  are  the  seven  bones  of  the  tarsus  /  at 
a  are  the  five  bones  of  the  meta-tarsus  •  and  at  b  and 
c  are  the  fourteen  bones  of  the  toes — twenty-six  in  alL 


Fi<».  51. 


The  reason  for  having  so  many  bones  in  the  foot  is 
the  same  as  that  stated  in  regard  to  the  hand  in  §  31. 
The  springiness  thus  given  to  the  foot  is  quite  im- 
portant in  guarding  against  shocks.  You  can  realize 
this  if  in  jumping  you  come  down  on  your  heels,  in- 
stead of  coming  down  on  your  feet  as  is  usually  done. 
Some  animals  that  leap  much  have  special  guards 
against  shocks  in  the  thick  elastic  cushions  on  the  bot- 
toms of  their  feet.  You  can  see  these  in  the  cat  and 
dog. 

37.  The  arched  form  of  the  foot  assists  in  giving 
springiness  to  it.  You  can  see  that  the  tread  is  much 
less  elastic  when  the  foot  happens  to  be  flat.  This 

How  many  bones  are  there  in  the  foot  ?  Why  are  there  so  many  ? 
"What  is  said  of  the  importance  of  elasticity  in  the  foot  ?  What  contriv- 
ances are  there  in  the  feet  of  some  animals  I 


128  FIRST   BOOK    IN    PHYSIOLOGY. 

arched  form  is  represented  in  Fig.  52,  which  gives  a 
side  view  of  the  bones  of  the  foot.     In  this  figure  the 
FIG.  52.  bones  of  the  tarsus  ex- 

tend from  the  heel  to  a  ; 
the  meta-tarsal  bones 
are  at  5  ;  and  the  bones 
of  the  toes  are  at  c.  In 
every  movement  of  the 
foot  there  is  some  little 
motion  between  all  these  bones,  and  it  is  this  that 
gives  ease  and  grace  to  its  motions.  Observe  what 
is  the  order  of  its  movement  in  walking.  The  heel 
first  touches  the  ground,  as  represented  in  the  figure. 
Then,  as  the  body  moves  forward,  the  ball  of  the 
foot  at  1}  presses  firmly  on  the  ground  as  the  heel 
rises.  Now,  as  the  change  of  pressure  is  made,  from 
the  heel  to  the  ball  of  the  foot,  there  is  a  little  giving 
between  all  the  bones  of  the  tarsus  a  and  the  meta- 
tarsus £,  and  this  makes  the  motion  an  easy  one.  If 
all  this  part  of  the  foot  were  one  bone,  the  motion 
would  be  stiff  and  awkward,  and  not  elastic  and 
graceful  as  it  now  is. 

38.  The  ends  of  all  the  bones  are  tipped  with  carti- 
lage so  that  they  can  move  easily  upon  each  other. 
And  besides  this,  the  ends  thus  tipped  with  this  fine 
bnt  smooth  substance  are  lined  with  a  very  fine  mem- 
brane, so  arranged  as  to  make  a  close  sac.  This  you 
can  understand  by  Fig.  53,  in  which  a  and  ~b  are  the 
ends  of  two  bones,  the  sac  o  being  represented  as  se- 

What  is  said  of  the  arched  form  of  the  foot?  Describe  the  movement 
of  the  foot  in  walking.  How  is  it  made  easy  and  graceful  ?  With  what 
are  the  ends  of  the  bones  tipped  ? 


THE   BONES.  129 


FIG.  53.  parated  from  the  bones,  in  order  that 
the  arrangement  may  be  clear  to  you. 
It  is  as  if  a  little  bladder  were  placed 
between  the  bones,  fastened  on  all 
over  the  two  surfaces  at  their  ends. 
This  bladder  or  sac  has  a  little  fluid  in 
it  like  the  white  of  an  egg.  This  fluid 
is  to  our  joints  what  oil  is  to  the  joints 
of  machinery.  When  a  train  of  cars 
stops  at  a  station  you  see  men  with 
their  little  cans  oil  the  boxes  of  the 
wheels  both  of  the  locomotive  and  the 
cars.  And  great  pains  is  taken  with  the  joints  of 
all  kinds  of  machinery  to  keep  them  oiled.  But 
the  joints  in  our  bodies  keep  themselves  oiled,  as  we 
may  say.  It  is  done  in  this  way :  The  fluid  in  the 
sac  of  a  joint  oozes  from  the  inner  surface  of  the  sac, 
just  as  the  perspiration  comes  from  the  pores  of  the 
skin.  But  the  same  fluid  does  not  remain  in  the 
joints  year  after  year.  Such  constant  rubbing  would, 
after  a  while,  make  it  unfit  for  use.  It  is,  therefore, 
constantly  renewed.  There  are  all  over  the  inside  of 
the  sac  little  absorbing  vessels  that  take  up  the  fluid 
as  fast  as  it  becomes  unfit  for  use,  and  there  are  secre- 
ting vessels  that  pour  out  fresh  fluid  to  take  its  place. 

What  other  provision  is  there  for  the  easy  working  of  the  joints  ? 
Compare  -with  common  machinery.  How  is  the  fluid  in  the  sacs  of  the 
joints  kept  fresh  ? 

6* 


130  FIRST   BOOK   IN    PHYSIOLOGY. 

CHAPTER    IX. 

THE  MUSCLES. 

1.  I  HAVE  already  explained  to  you  in  Chapter  II. 
the  manner  in  which  the  muscles  act.     You  there  saw 
that  when  a  muscle  acts,  its  fibres  all  shorten  them- 
selves.    Now,  when  a  muscle  contracts  or  shortens 
itself,  it  swells  out  or  becomes  thicker.     You  can  see 
this  if  you  watch  the  bare  arm  of  some  one  who  is  at 
work.     You  can  feel  this  swelling  of  the  muscles  in 
your  own  arm  as  you  move  it.     Straighten  out  your 
arm,  and  then  grasp  it  wTith  your  other  hand  half-way 
from  the  elbow  to  the  shoulder.     Now  bend  up  your 
arm  forcibly,  and  you  will  feel  the  large  muscle  on 
the  front  of  your  arm  swell  out  and  harden  as  you 
grasp  it.     It  is  just  as  it  is  with  a  piece  of  india-rub- 
ber.    If  you  stretch  out  the  india-rubber,  it  becomes 
smaller ;  and  then  if  you  let  it  go,  it  contracts  like  the 
muscle,  and  as  it  contracts,  it,  like  the  muscle,  becomes 
thick  again. 

2.  The  muscle,  however,  contracts  in  this  case  from 
a  different  cause  than  that  which  makes  the  india- 
rubber  contract.     The  india-rubber  contracts  because 
it  is  stretched — it  merely  goes  back  to  its  usual  state 
by  its  elasticity, .  as  it  is  termed.     But  the  muscle  has 
a  power  of  contracting  which  is  something  more  than 
elasticity.     It  contracts  because  the  mind  tells  it  to 
do  so  by  means  of  the  nerves,  the  telegraphic  wires 

What  is  the  state  of  a  muscle  when  it  contracts  ?  Make  the  compar- 
ison between  the  muscle  and  india-rubber.  How  do  they  differ  from 
each  other  in  the  causes  of  their  contraction  ? 


THE  MUSCLES.  131 


that  go  from  the  mind's  seat,  the  brain.  The  nerves, 
as  I  have  told  you  in  the  chapter  on  the  Nervous  Sys- 
tem, branch  out  and  distribute  their  fibres  to  all  the 
fibres  of  the  muscles.  And  every  fibre  of  a  muscle 
thus  receives  a  message  from  the  brain  whenever  the 
muscle  contracts. 

3.  The  muscles  have  elasticity,  just  as  the  india- 
rubber  has,  and  there  is  a  contraction  in  them  by 
means  of  this  elasticity.     This  is  seen  when  a  muscle 
is  cut  in  two,  by  accident,  or,  as  is  sometimes  done,  in 
the  operations  of  the  surgeon.  In  this  case  the  two  cut 
ends  separate  from  each  other  considerably,  because 
they  are  drawn  apart  by  the  contraction  of  the  fibres 
of  the  muscle.     But  this  contraction  does  not  take 
place  from  any  message  sent  to  these  fibres  from  the 
mind.     It  arises  from  their  elasticity  simply,  just  as 
the  contraction  of  the  india-rubber  arises  from  its 
elasticity.     Muscles,  then,  have  two  kinds  of  contrac- 
tion.    The  one  kind  is  from  their  elasticity  ;  the  other 
is  when  they  are  excited  to  action  through  the  nerves. 
I  shall  speak  of  these  two  kinds  of  contraction  in  an- 
other part  of  this  chapter. 

4.  Muscles  commonly  end  in  tendons.     While  the 
muscles  are  red,  the  tendons  are  white  and  shining. 
Tendons  are  the  ropes  or  rigging  with  which  the  mus- 
cles pull  the  bones  and  other  parts.     They  are  of  dif- 
ferent shapes.     Some  of  them  are  long  and  slender. 
You  can  see  tendons  of  this  shape  on  the  back  of  the 
hand  very  plainly  in  thin  persons.     The  muscles  that 
work  them  are  in  the  full  arm  above.     You  can  see 

Show  how  the  muscles  have  two  kinds  of  contraction.      What  are 
tendons  ?     What  is  said  of  their  shape  ? 


132  FIRST   BOOK   IN    PHYSIOLOGY, 

that  this  is  so,  if  while  you  work  your  fingers  back 
and  forth,  you  take  hold  of  the  arm  a  little  below  the 
elbow  with  the  other  hand.  You  feel  very  distinctly 
there  the  movement  of  the  muscles  as  they  contract 
and  relax  themselves. 

5.  The  tendons  are  much  smaller  than  the  muscles 
that  pull  them.     You  can  see  this  in  the  case  of  the 
hand  and  arm.     The  muscles  that  move  the  hand  and 
the  fingers  make  up  the  full  part  of  the  arm ;  but  the 
wrist,  where  their  tendons  go  to  the  hand,  is  very  slen- 
der, because  these  tendons  are  so  small.     You  can  see 
the  same  thing  in  the  "  drumstick"  of  a  fowl.     In  the 
slender  leg  are  the  tendons  lying  along  the  bone, 
while  the  bulky  muscles  that  work  them  are  above. 

6.  While  the  tendons  are  so  small,  they  are  very 
strong.     It  is  exceedingly  rare  to  have  them  break, 
even  in  the  most  violent  efforts.     It  is  well  that  it  is 
so,  for  it  is  very  difficult  to  heal  a  broken  tendon. 
When  a  bone  is  broken,  the  two  ends  can  be  held 
accurately  together,  and  therefore  are  easily  united. 
But  when  a  tendon  is  broken  the  muscle  to  which  it 
belongs  draws  the  part  that  is  fastened  to  it  away 
from  the  other  end.     And,  therefore,  with  the  very 
best  of  care,  it  is  difficult  to  make  them  heal  at  all. 

7.  I  will  now  speak  particularly  of  some  of  the 
muscles,  that  you  may  understand  how  they  act.     In 
Fig.  54  is  represented  the  lower  part  of  the  large 
muscle  that  raises  the  heel  when  we  walk.     The  large 
bone  of  the  leg  and  the  bones  of  the  foot  are  repre- 
sented.   P,  the  muscle,  makes  up  most  of  the  bulk  of 

What  is  said  of  the  size  of  the  tendons  ?     What  of  their  strength  ? 
Why  is  it  difficult  to  heal  a  broken  tendon  I 


THE  MUSCLES. 


133 


FIG.  54. 


the   calf  of    the  leg. 

The  weight  of  the  body 

rests  upon  the  bone  W. 

Now,  in  walking,   as 

we  raise  the  body  in 

taking  a  step,  we  do 

it  first  by  raising  the 

heel  with  the  muscle 

p,  the  pressure  being 

on    the    ball    of    the 

foot,  F.     This  muscle  does  here  with  the  weight  of  the 

body  what  the  muscles  of  your  arms  do  to  the  load  in 

a  wheelbarrow  when  you  raise  it  by  the  handles. 

8.  In  Fig.  55  are  represented  two  of  the  principal 
muscles  of  the  arm,  4  and  7.  Between  these  is  the 
bone  of  the  arm,  1,  and  at  2  are  the  bones  of  the  fore- 
arm, as  the  part  of  the  arm  below  the  elbow  is  com- 
monly called.  At  4  is  the  muscle  that  acts  when  you 

FIG.  55. 


bend  the  arm  at  the  elbow.    At  5  is  its  double  attach- 
ment at  the  shoulder-joint,  and  at  6  is  where  its  ten- 
Describe  the  arrangement  and  action  of  the  muscle  represented  in 
Fig.  54.     Describe  the  muscles  represented  in  Fig.  55. 


134  FIRST    BOOK    IN    PHYSIOLOGY. 

don  is  fastened  to  the  radius,  one  of  the  bones  of  the 
fore-arm.  I  have  described  the  manner  in  which  this 
muscle  acts  in  Chapter  II.  §  10.  The  muscle  that  acts 
in  opposition  to  this,  and  straightens  the  arm  out,  is 
at  7,  and  is  fastened  at  8  to  the  point  of  the  elbow. 
"When  you  bend  and  straighten  your  arm  by  turns, 
these  two  muscles  take  turns  in  acting,  like  two  saw- 
yers that  are  working 'a  long  saw  back  and  forth. 
While  one  sawyer  pulls,  the  other  lets  the  saw  go.  So 
it  is  with  these  muscles.  "When  the  muscle  4  contracts, 
the  muscle  7  is  relaxed ;  and  when  7  contracts,  4  is  re- 
laxed. And  so  it  is  with  other  muscles.  Thus,  when 
you  swing  your  leg  back  and  forth,  there  are  two  sets 
of  muscles  that  perform  these  two  opposite  motions, 
and  while  one  set  are  contracting,  the  other  are  relax- 
ing. So  it  is  with  the  motion  of  the  lower  jaw  up 
and  down  in  eating.  While  the  muscles  that  move 
it  up  are  contracting,  those  that  pull  it  down  are  re- 
laxed; and  then,  while  those  that  pull  it  down 
contract,  those  that  draw  it  up  are  relaxed. 

9.  In  Fig.  56  you  see  represented  some  of  the  mus- 
cles of  the  face  and  the  neck.  At  5  is  a  large,  spread- 
ing, fan-shaped  muscle,  which,  with  another  muscle, 
c,  raises  the  lower  jaw,  in  eating.  You  can  perceive 
the  action  of  this  muscle,  if  you  place  your  fingers 
on  the  temple  of  either  side,  while  you  move  the 
jaw  up  and  down.  This  is  quite  a  large  and  pow- 
erful muscle.  Observe,  how  well  it  is  packed  over 
the  side  of  the  head,  so  as  to  make  no  uncomely 

Give  the  comparison  made  in  regard  to  their  action.  "What  other 
illustrations  are  given  of  opposite  motions  in  muscles  ?  Describe  the 
muscles  represented  in  Fig.  66,  and  explain  their  operation. 


THE    MUSCLES. 


135 


projection  there.  For  this 
purpose,  it  is  shaped  very 
differently  from  the  mus- 
cles of  the  arm  in  Fig.  55.  a 
There  are  some  other  mus- 
cles in  this  figure,  which 
I   will   barely    notice. — 
There  is  at  a  a  small  mus-  c_... 
cle,  which,  coming  from  ^_ 
the  bone  at  the  top  of  the    a- 


When  it  contracts,  it  / 
wrinkles  the  eye-brow. —  M 
At  g  is  a  muscle  that 
draws  up  the  corner  of 
the  mouth,  and  at  /  is  a  muscle  that  draws  down 
the  lower  lip.  At  d  is  a  muscle  which  serves  several 
purposes.  It  pulls  back  the  corner  of  the  mouth  ;  and 
when  we  are  eating,  by  pressing  the  food  towards  the 
middle  of  the  mouth,  keeps  it  from  getting  outside  of 
the  teeth.  When  one  blows  upon  an  instrument 
strongly,  this  muscle  gives  firmness  to  the  cheek,  so 
that  the  air  shall  not  press  it  out  too  much.  From 
its  doing  this,  it  is  called  ~buccinator,  from  buccinare, 
to  blow  a  trumpet. 

10.  At  A,  in  Fig.  56,  you  see  a  long  muscle,  which 
begins  just  behind  the  ear,  and  goes  down  to  the  top 
of  the  breast-bone.  You  see  another  muscle  on  the 
other  side  of  the  neck  exactly  similar  to  it.  This  pair 
of  muscles  is  very  plainly  seen  in  the  neck  of  a  thin 

Explain  the  action  of  two  muscles  in  the  neck  in  bowing  the  head 


136  FIRST   BOOK    IN    PHYSIOLOGY. 

person.  When  they  contract  together,  you  bow  the 
head  forward.  If  they  contract  exactly  alike,  you 
bow  your  head  straight  forward.  But  if  one  of  them 
acts  more  than  the  other,  then  you  bow  your  head  in 
a  one-sided  way.  If  you  observe  persons  as  they  bow 
to  those  whom  they  pass,  you  will  see  that  they  often 
bow  more  or  less  in  a  one-sided  way.  That  is,  one  of 
these  muscles  pulls  upon  the  head  harder  than  the 
other  does.  In  some,  this  unequal  action  of  this  pair 
of  muscles  becomes  a  habit. 

11.  Observe  now  what  a  variety  of  motions  can  be 
produced  by  these  two  muscles  alone.  First,  the 
extent  to  which  you  bow  the  head  forward  can  be 
varied  to  any  degree  you  please,  by  varying  the 
degree  of  the  contraction  of  these  muscles.  When 
you  bow  your  head  forward  very  much  they  contract 
strongly ;  and  when  you  bow  it  forward  but  little, 
they  contract  slightly.  And  their  contraction,  can 
vary  in  all  degrees  between  the  greatest  and  the 
slightest.  So  also  the  direction  in  which  the  head  is 
bowed  can  be  varied  to  any  extent  you  please.  You 
can  bow  the  head  in  any  direction,  either  to  the  right 
or  left,  by  varying  the  inequality  of  the  action  of  the 
two  muscles.  If  you  bow  your  head  very  much  to 
one  side,  you  make  one  of  them  contract  much  more 
strongly  than  the  other.  But  if  you  incline  the  head 
only  a  little  towards  one  side,  the  muscle  of  that  side 
contracts  only  a  little  more  than  that  of  the  other  side. 
And  the  inequality  in  their  contraction  can  be  varied 
in  all  degrees  between  the  smallest  degree  and  the 

Show  the  variety  of  motion  that  can  be  made  by  them  in  two  ways 
— in  regard  to  the  extent  and  the  direction  of  the  motion. 


THE    MUSCLES.  137 


greatest.  You  will  realize  the  truth  of  what  I  have 
told  you  in  this  paragraph,  if  you  try  the  experiment 
on  yourself,  and  observe  how  much  you  can  vary  the 
bowing  of  your  head  both  in  extent  and  direction. 

12.  Now,  if  so  much  variety  of  motion  can  be  pro- 
duced by  only  two  muscles,  how  great  is  the  variety 
when  there  are  many  muscles  in  action,  each  of  which 
can  have  its  contraction  varied  in  all  degrees.     You 
see  this  well  illustrated  in  the  hand  and  arm.     Raise 
your  hand,  and  think  what  the  muscles  do  when  you. 
perfqrm  this  motion.     Although  it  seems  to  you  so 
simple  a  motion,  many  muscles  are  engaged  in  per- 
forming it.     And  each  one  of  these  muscles  has  its 
particular  part  to  do  in  making  the  motion.    In  doing 
its  part  it  must  contract  just  enough.     If  it  pull  too 
much,  or  too'  little,  it  will  interfere  with  the  action  of 
the  other  muscles,  and  there  will  be  a  failure  in  the 
motion.     But  there  is  no  such  failure.     All  the  mus- 
cles contract  just  enough,   and  the  hand  is   raised 
exactly  as  the  mind  directs.     JSTow,  if  you  raise  it 
again  in  a  little  different  position,  all  these  muscles 
act  in  a  little  different  way.     And  you  can  go  on  to 
raise  it  in  a  great  variety  of  ways,  altering  the  height 
and  direction  each  time  by  altering  the  action  of  all 
these  muscles. 

13.  At  the  same  time  that  you  vary  the  motion  of 
the  hand,  you  can  also  vary  to  almost  any  extent  the 
motions  of  the  fingers,  by  the  varied  action  of  the 
muscles  that  work  them.     You  can  get  some  idea  of 


What  is  said  of  the  variety  of  motion  -when  many  muscles  act  to- 
gether? Illustrate  by  referring  to  the  hand.  What  is  said  of  the 
exact  manner  in  which  each  muscle  does  its  part  ? 


138  FIRST   BOOK   IN    PHYSIOLOGY. 

tlie  variety  of  these  motions  if  you  watch  a  person 
that  is  writing,  or  one  that  is  playing  on  a  piano.  For 
every  one  of  these  exceedingly  varied  motions  there 
must  be  a  variation  of  the  action  of  a  great  number 
of  muscles.  Each  muscle  must  in  every  motion  per- 
form its  particular  part  exactly  right,  or  there  will  be 
an  interference  with  the  action  of  the  other  muscles, 
and  consequently  a  failure  in  the  motion.  But,  com- 
monly each  muscle  contracts  exactly  right,  and  so 
each  one  of  the  motions  that  so  rapidly  follow  each 
other  is  performed  just  as  the  mind  directs. 

14.  If  you  examine  some  of  the  motions  performed 
by  the  fingers,  that  appear  very  simple,  you  will  see 
that  they  are  performed  by  a  very  complicated  ma 
chinery.     Take,  for  instance,  that  seemingly  simple 
movement  made  in    buttoning   your   coat.     If  you 
watch  the  fingers,  as  they  put  the  button  through  the 
button-hole,  you  will  see  that  the  movement  is  quite 
a  complicated  one.     It  is  so  much  so,  that  no  man 
could  make  a  machine  in  the  shape  of  the  hand  that 
could  perform  it.     And  the  same  can  be  said  of  other 
motions. 

15.  The  tongue  exhibits  great  variety  in  its  motions. 
If  you  stand  before  a  glass,  and,  opening  your  mouth, 
move  about  your  tongue  rapidly,  it  looks  as  if  some 
little  tricksy  spirit  were  in  it  playing  on  its  fibres. 
But  each  of  these  fibres  is  put  exactly  in  its  right 
place,  and  contracts  exactly  aright  in  all  the  varied 


"What  is  said  of  the  variation  of  the  motions  of  the  hand  and  fingers 
in  such  actions  as  writing,  or  playing  on  a  piano  ?  What  is  said  of 
some  apparently  simple  motions  of  the  fingers  ?  What  is  said  of  the 
movements  of  the  tongue,  and  of  the  arrangement  of  its  fibres  ? 


THE   MUSCLES.  139 


motions  of  this  organ,  as  we  use  it  in  speaking,  and 
eating,  and  swallowing. 

16.  The  act  of  swallowing  seems  to  you  a  very 
simple  thing,  but  it  is  really  a  complicated  act  of  a 
complicated   set    of  machinery.       There  are   many 
muscles  that  work  together  in  doing  it,  and  if  they 
did   not  work  right  there  would  be   failure  in  the 
motion,  and  choking  would  result.     Observe  that  dif- 
ferent   muscles  work  in  different  parts  of  the  act. 
When  you  first  begin  the  act,  the  food  is  thrust  back 
chiefly  by  the  muscles  of  the  tongue.     As  it  goes 
back,  the  epiglottis,  the  lid  of  the  larynx,  is  shut 
down  by  its  muscles,  so  that  the  food  may  slide  over 
it  into  the  oesophagus  that  lies  behind  the  windpipe. 
This  lid,  which  thus  shuts  over  the  top  of  the  passage 
to  the  lungs  when  we  swallow,  is  raised  up  by  its 
muscles  when  we  speak  or  breathe.     It  is  like  a  little 
tongue  extending  back  from  the  root  of  the  tongue 
itself.     After  the  food  has  passed  over  this  lid  it  goes 
down  through  the  oesophagus  into  the  stomach.     But 
it  does  not  simply  fall  down.     The  oesophagus  is  a 
tube,  made  in  part  of  muscular  fibres,  so  arranged 
that  the  food  is  really  pushed  by  their  action  through 
this  tube.     So  complicated  is  all  this  machinery,  and 
so  nice  is  its  operation,  that  it  would  be  impossible 
for  any  man  to  make  a  machine  of  the  same  sfiape 
that  could  perform  the  act  of  swallowing. 

17.  It  seems  to  you  a  simple  thing  to  speak.     But 
every  time  that  you  speak  there  is  a  large  number  of 
muscles  brought  into  action.     There  are  the  muscles 

What  is  said  of  the  act  of  swallowing  ?     Describe  the  different  parts 
of  this  act 


140  FIRST    BOOK    IN    PHYSIOLOGY. 

of  the  chest  that  force  the  air  out  through  the  wind- 
pipe— the  muscles  that  move  the  cords  in  the  music- 
box,  the  larynx — the  muscles  that  move  the  epiglot- 
tis, the  lid  of  the  larynx — and  the  muscles  that  move 
the  palate,  the  tongue,  the  jaws,  and  the  lips.  You 
cannot  utter  a  word  without  the  action  of  all  these 
different  muscles.  And  they  must  act  just  right,  or 
there  would  be  something  wrong  in  the  sound  of  the 
word. 

18.  As  the  different   acts   of  speaking,  laughing, 
breathing  and  swallowing  follow  each  other  so  rapidly, 
there  is  vast  variety  in  the  changing  action   of  the 
muscles.    Especially  busy  are  those  little  muscles  that 
work  the   lid   of  the   larynx,  opening  it  when  we 
breathe,  or  speak,  or  laugh,  and  shutting  it  down 
when  we  swallow.     So  securely  do  these  door-keepers 
guard  this  door  to  the  windpipe,  that  it  is  a  rare  acci- 
dent for  a  crumb  or  a  drop  to  get  into  it. 

19.  In  performing  the  different  motions  that  I  have 
alluded  to,  such  as  swallowing,  speaking,  and  the  mo- 
tions of  the  hand,  there  must  be  a  concert  or  agree- 
ment of  action  among  the  muscles.     The  concert  is 
as  real  as  it  would  be  if  the  muscles,  like  men  that 
are  pulling  at  ropes,  understood  each  other,  and  agreed 
together  as  to  what  they  would  do.     It  is,  indeed,  a 
more   perfect   concert    of   action   than    ever   occurs 
among  a  company  of  men  in  pulling  ropes,  especially 
when  they  pull  upon  different  ropes.     It  is  difficult 

"What  different  Bets  of  muscles  are  engaged  in  the  act  of  speaking  ? 
What  is  said  of  the  variety  of  muscular  action  as  we  speak  and  breathe 
and  laugh  and  swallow  almost  at  the  same  time  ?  What  muscles  are 
then  especially  busy  ?  What  is  said  of  the  concert  of  action  in  the 
muscles  ? 


THE   MUSCLES.  141 


for  each  man  to  pull  just  enough  and  at  exactly  the 
right  time.  But  there  is  no  difficulty  of  this  sort 
commonly  with  the  muscles,  however  complicated 
the  action  may  be.  Thus  in  swallowing,  each  muscle 
acts  just  strongly  enough  and  exactly  at  the  right 
time. 

20.  I  will  now  give  you  a  general  view  of  the  mus- 
cles of  the  body.     In  Fig.  57  you  have  a  side  view  of 
the  muscles,  that  is,  of  all  those  that  lie  directly  under 
the  skin.     There  are  many  other  muscles  that  lie  un- 
der these  that  you  see.    You  observe  that  the  muscles 
are  of  various  shapes  and  sizes,  according  to  their 
situation  and  what  they  are  intended  to  do.  They  are 
round,  flat,  long,  short,  fan-shaped,  circular,  &c.     I 
will  notice  some  of  them  particularly. 

21.  At  a  is  a  very  large  muscle  at  the  top  of  the 
shoulder,  that  raises  the  arm,  at  the  same  time  carry- 
ing it  out  from  the  body.     At  5  is  the  muscle  that 
bends  the  fore-arm  at  the  elbow.     At  e  is  the  muscle 
that  acts  in  opposition  to  b  and  straightens  the  arm. 
The  muscles  at  5  and  e  are  the  same  as  those  at  4  and 
7  in  Fig.  55.     At  d  is  a  muscle  that  turns  the  fore- 
arm in  such  a  way  that  the  palm  of  the  hand  is  up- 
ward, as  seen  in  the  figure.     At  g  is  a  very  large  mus- 
cle.    It  comes  from  almost  the  whole  length  of  the 
back-bone,  and  its  tendon  is  fastened  to  the  back  part 
of  the  arm.     Its  office  is  to  draw  the  arm  back.      Its 
tendon  makes  the  rear  boundary  of  the  arm-pit.     At 
i  is  one  of  the  large,  flat  muscles  of  the  abdomen.     At 
I  and  k  are  two  muscles  that  move  the  thigh.     At  o 

Describe  the  muscles  of  the  body  as  represented  in  Fig.  57. 


142  FIRST   BOOK    IN   PHYSIOLOGY. 


and  p  on  the  right  thigh,  and  at  n  on  the  left,  are  seen 
three  muscles  that  serve  to  throw  the  leg  forward. 
They  do  this  by  pulling  on  the  knee-pan.  At  q  is  the 


THE   MUSCLES.  143 

tendon  that  forms  the  outer  hamstring,  and  at  r  are 
the  two  tendons  that  form  the  inner  one.  The  mus- 
cles that  pull  these  hamstrings  are  on  the  back  part 
of  the  thigh.  When  they  act  they  make  the  leg 
swing  backward,  and  therefore  do  just  the  opposite  of 
what  is  done  by  the  muscles  n,  o  and  p.  At  6-  is  the 
musele  that  makes  the  back  of  the  calf  of  the  leg.  Its 
strong  tendon,  which  is  fastened  to  the  bone  of  the 
heel,  you  can  feel  very  plainly  through  the  skin.  It 
is  this  muscle,  a  part  of  which  is  represented  in  Fig. 
54,  at  P. 

22.  The  muscles  differ  greatly  in  size.     Some  are 
very  large,  and  some  are  exceedingly  small.     Con- 
trast, for  example,  the  muscles  of  the  arm  that  wield 
the  hammer  and  the  axe,  with  the  muscles  that  move 
the   cords   of  the  larynx   in  speaking  and  singing. 
These  muscles  of  the  voice  are  very  delicate,  and  they 
produce  the  various  notes  by  motions  so  small,  that 
many  of  them  could  be  measured  by  the  breadth  of 
a  hair.    Birds  that  mount  up  so  beautifully  in  the  air, 
have  large  muscles  to  work  their  wings.     But  the 
muscles  that  move  their  little  musical  cords,  as  they 
carol  so  sweetly,  are  so  small,  that  it  is  difficult  to  find 
them  when  we  dissect  the  larynx. 

I  will  now  notice  some  especial  contrivances  in  the 
muscles  and  tendons. 

23.  There  is  a  beautiful  arrangement  of  the  ten- 
dons in  the  toes  and  the  fingers.     In  Fig.  58  is  a  rep- 
resentation of  this  arrangement  in  one  of  the  fingers. 
At  <z,  I  and  <?,  are  the  three  bones  of  the  finger.    At/* 

"What  is  said  of  the  size  of  the  muscles?     Give  the  contrasts  men- 
tioned. 


144  FIRST   BOOK    IN    PHYSIOLOGY. 

FIG.  58. 


a 


is  the  tendon  that  bends  the  second  bone,  ~b.  This  is 
divided  into  two  parts,  as  you  see,  just  at  it§  end, 
where  it  is  fastened  to  the  bone.  Through  this  divi- 
sion the  tendon  e  passes,  to  go  to  the  last  bone,  c.  In 
the  Figure  the  tendons  are  raised  up  so  that  you  may 
see  the  arrangement  clearly.  This  arrangement  is 
seen  in  each  of  the  fingers  and  in  each  of  the  toes. 

24.  There  is  a  very  curious  contrivance  in  the  sole 
of  the  foot.  There  is  a  muscle  in  the  calf  of  the  leg, 
from  which  there  comes  down  a  tendon  that  is  divided 
into  four,  for  the  purpose  of  bending  the  toes.  Now, 
there  is  a  short  muscle  in  the  bottom  of  the  foot  that 
sends  four  tendons  to  join  those  that  come  down  from 
the  muscle  in  the  leg,  so  as  to  help  them  pull  the  toes. 
The  reason  for  this  arrangement  is  this.  If  all  the 
muscle  that  is  needed  to  pull  the  toes  were  to  be  put 
into  the  sole  of  the  foot,  it  would  make  the  foot  too 
large  at  that  part  ;  so  the  thing  is  done  with  two  mus- 
cles, put  in  different  places,  instead  of  one  muscle.  It 
is  the  same  sort  of  contrivance  with  that  to  which  a 
man  would  resort,  if  he  wished  to  move  something 
with  ropes,  manned  by  a  company  of  men,  but  could 
not  conveniently  get  men  enough  into  one  spot  to  do 
it.  He  would  fix  some  other  ropes  in  another  spot,  in 


Describe  the  arrangement  of  tendons  represented  in  Fig.  68.  Describe 
the  arrangement  of  muscle  and  tendons  in  the  sole  of  the  foot.  Give  the 
comparison  made  in  regard  to  it. 


THE   MUSCLES.  145 


such  a  way  that  a  second. company  of  men  could  help 
the  first.  This  short  muscle  in  the  sole  of  the  foot  has 
received  the  singular  name  of  massa  carnea  Jacobi 
Sylvii—ih&t  is,  the  fleshy  mass  of  James  Sylvius,  the 
anatomist  who  first  pointed  out  this  arrangement. 

25.  We  have  many  examples  of  tendons  working 
with  a  pulley-arrangement.     This  is  the  case  with  the 
tendons  that  go  from  the  muscles  in  the  leg  to  the 
foot.     They  are   bound  down   by  ligaments  at  the 
ankle,  and  work  under  them,  just  as  a  rope  works 
through  a  pulley.     If  it  were  not  for  these  ligaments 
the  tendons  would  fly  out  continually  when  the  mus- 
cles acted,  making  projecting  cords  under  the  skin. 
There  are  similar  ligaments  at  the  wrist. 

26.  There   is  a  beautiful  example  of  the  pulley- 
arrangement  in  the  eye,  which  you  see  in  Fig.  59. 

Fin.  59. 


There  are  six  muscles  that  move  the  eye-ball.  Five 
of  them  are  represented.  There  are  four  straight 
muscles.  Three  of  them  are  marked  &,  b  and  c.  You 
see  just  the  upper  edge  of  the  fourth  one  behind  I. 
These  muscles  come  from  the  back  part  of  the  socket 
of  the  eye,  and  have  tendons  that  are  fastened  to  the 

What  is  the  pulley-arrangement  at  the  ankle  and  "wrist?     Describe 
the  muscles  of  the  eye-ball  as  given  in  Fig.  59. 


146  FIRST    BOOK    IN    PHYSIOLOGY. 

eye-ball.  The  muscle  a,  when  it  contracts,  turns  the 
eye  upward  ;  c  turns  it  downward  ;  ~b  turns  it  to  one 
side,  and  its  opposite  muscle  turns  it  to  the  other  side. 
But  there  are  some  other  rolling  motions  of  the  eye 
that  are  performed  by  two  oblique  muscles,  as  they 
are  called.  One  of  these,  *,  is  represented.  It  has  a 
long  tendon,  which  passes  through  a  ring  in  the  car- 
tilage in  the  roof  of  the  socket,  and  then  turning 
back  is  fastened,  as  you  see,  to  the  upper  part  of  the 
eye-ball. 

FIG.  60. 


27.  I  will  notice  one  more  example  of  the  applica- 
tion of  the  pulley.  It  is  in  the  case  of  the  muscle 
that  draws  down  the  lower  jaw,  represented  in  Fig. 
60.  It  is  in  reality  two  muscles.  One,  a,  is  attached 
to  the  bone  behind  the  ear,  and  the  other,  5,  is 
attached  to  the  inside  of  the  chin.  They  join  together 
by  a  tendon  ;  and  this  tendon,  as  you  see,  works  in  a 
loop,  as  a  rope  does  in  a  pulley.  You  can  see  that 
when  these  two  muscles,  a  and  5,  contract,  they  draw 

Describe  the  arrangement  of  the  muscle  tbat  pulls  down  the  lower 
jaw. 


THE    MUSCLES.  147 


down  the  jaw.  Now  observe,  that  the  jaw  could  be 
drawn  down  in  a  much  more  simple  way  than  this. 
It  could  be  done  by  a  muscle  going  straight  from  the 
chin  to  the  top  of  the  breast-bone.  But  this  would 
make  the  neck  look  very  ugly,  and  hence  this  pulley- 
arrangement  was  adopted.  The  machinery  that 
draws  down  the  jaw  is  in  this  way  kept  out  of  sight, 
and  so  does  not  interfere  with  the  beautiful  shape  of 
the  neck. 

28.  This  regard  to  beauty  of  shape,  so  manifest  in 
the  arrangement  of  this  muscle  in  the  neck,  may  be 
observed  in  the  arrangement  of  the  muscles  generally. 
They  are  so  arranged,  for  example,  in  the  limbs,  as 
to   give    to   them   a  graceful   shape.     The  muscles 
which  move  the  hand  and  the   fingers   are   mostly 
placed  in  the  arm,  giving  to  it  the  full  and  flowing 
outline  which  makes  it  so  beautiful.     If  they  were 
placed  in  the  hand,  where  they  do  their  work,  the 
hand  would  be  a  very  clumsy  instrument.     I  could 
give  many  other  examples,  but  these  are  sufficient. 

29.  You  see  that  there  are  in  the  body,  in  its  two 
halves,  two  sets  of  muscles  that  are  alike,  just  as  it  is 
with  the  two  halves  of  the  brain  and  the  two  sets  of 
nerves.    The  exact  equality  of  the  two  sets  of  muscles 
is  strikingly  exemplified  in  the  muscles  of  the  mouth. 
The  mouth  is  held  in  the  middle  of  the  face,  because 
the  muscles  on  each  side  of  it  are  exactly  alike,  and 
pull  alike  upon  its  two  corners.    If  the  muscles  on  one 


What  is  the  need  of  this  peculiar  arrangement?  What  is  said  of  re- 
gard to  beauty  in  the  arrangement  of  the  muscles  ?  "What  is  said  of  the 
two  sets  of  muscles  in  the  two  halves  of  the  body  ?  How  is  the  mouth 
held  in  the  middle  of  the  face  ? 


148  FIRST   BOOK    IN    PHYSIOLOGY. 

side  were  stronger  than  those  on  the  other,  the  mouth 
would  be  drawn  to  the  side  of  the  strongest.  Some- 
times the  muscles  on  one  side  of  the  face  are  palsied, 
and  then  the  mouth  is  drawn  to  the  other  side. 

30.  When  the  face  is  palsied  upon  one  side,  the 
two  kinds  of  contraction  that  I  noticed  in  §  3  are  well 
illustrated.     "When  the  muscles  of  the  face  are  quiet, 
the  difference  between  the  two  sides  is  not  very  great. 
For  the  muscles  are  then  only  under  the  influence  of 
their  elasticity,  and  this  is  not  much  less  in  the  pal- 
sied  muscles   than   in  the   opposite   ones.     But   the 
moment  that  the  muscles  are 'excited  to  contraction 
by  the  nerves,  as  in  speaking  or  laughing,  the  mouth 
is  drawn  very  much  to  one  side,  giving  the  face  a . 
very  odd  appearance. 

31.  Sometimes  muscles  are  for  some  reason  perma- 
nently contracted,  and  thus  cause  deformity.    Squint- 
ing is  produced  in  this  way.     The  straight  muscle  on 
one  side  of  the  eye-ball  contracts  more  strongly  than 
the  straight  muscle  on  the  opposite  side.    Thus,  if  the 
eye  turns  in  towards  the  nose,  the  inner  muscle  con- 
tracts more  strongly  than  the  outer  one. 

32.  The   expression   of  the   countenance   depends 
entirely  upon  the  action  of  muscles.     The  chief  of 
these  muscles  of  expression  are  those  that  wrinkle  the 
eye-brows,  and  those  that  pull  up  and  pull  down  the 
corners  of  the  mouth.     When  one  laughs,  the  corners 
of  the  mouth  are  drawn  up,  as  seen  in  Fig.  61^    But 
when  one  cries  or  is  very  sad,   the  corners   of  the 

What  is  said  of  the  two  kinds  of  contraction  when  the  face  is  palsied 
on  one  side  ?  How  is  squinting  produced  ?  Upon  what  does  the  ex- 
pression of  the  countenance  depend  ?  What  muscles  are  the  chief  agents 
of  expression  ? 


THE   MUSCLES. 


149 


Fio.  61. 


mouth  are  drawn  down.  In  laughing,  the  muscles 
draw  up  the  corners  of  the  month  so  strongly  as  to 
push  up  the  cheeks  and  wrinkle  the  skin  under  the 
eyes;  but  in  smiling,  the  muscles  raise  the  corners  of 
the  mouth  but  slightly.  The  eyes  seem  to  smile,  but 
they  do  not.  It  is  the  effect  wholly  of  the  action  of 
the  little  muscles  that  raise  the  corners  of  the  mouth. 
33.  In  Fig.  62  there  is  an  action  of  the  muscles  of 
expression  entirely  different  from  that  in  Fig.  61. 
Here  is  an  expression  of  jealous,  peevish  melancholy. 
The  corners  of  the  mouth  are  drawn  down,  and  the 
eye-brows  are  wrinkled  by  the  muscle  #,  repre- 
sented in  Fig.  56.  This  makes  the  eyes  look  cross. 
Now,  if  the  eyes  remained  just  the  same,  and  the 
muscles  that  wrinkle  the  eye-brows  and  those  that  pull 

Explain  the  action  of  the  muscles  in  Figs.  61  and  62. 


150  FIRST   BOOK    IN   PHYSIOLOGY. 


FIG.  62. 


down  the  corners  of  the  mouth  were  relaxed,  the  eyes 
would  look  pleasant.  This  subject  of  the  expression 
of  the  countenance  I  treat  in  full  in  my  larger  work 
on  Physiology. 

34.  I  have  spoken  mostly  of  those  muscles  that  act 
in  obedience  to  our  will.  These  are  called  voluntary 
muscles,  and  they  are  excited  to  act  through  nerves 
that  come  from  the  brain.  The  muscles  of  our  limbs, 
for  example,  are  excited  to  act  through  the  nerves 


THE   MUSCLES.  151 


that  come  to  them  from  the  brain  when  the  mind 
wills  them  to  act.  But  there  is  another  class  of  mus- 
cles that  act  without  our  willing  them  to  do  so.  They 
are  called  involuntary  muscles.  The  heart,  for  exam- 
ple, is  a  bundle  of  muscles,  that  are  always  acting 
without  being  told  by  the  mind  to  act.  As  the  stom- 
ach churns  the  food,  as  mentioned  in  §  13,  in  Chap- 
ter HI.,  the  will  has  nothing  to  do  with  the  contrac- 
tion of  its  muscular  coat.  And  so  the  muscles  of 
breathing  keep  at  work  without  being  told  to  do  so  by 
the  will. 

35.  These  involuntary  muscles,  then,  are  parts  of 
the  muscular  machinery  that  do  not  depend  upon  the 
mind  to  make  them  act.     They  act  when  the  mind  is 
asleep  as  well  as  when  it  is  awake.    While  the  volun- 
tary muscles  are  resting,  some   of  the  involuntary 
muscles  are  ever  at  work.    The  heart  is  always  pump- 
ing the  blood,  and  the  muscles  of  breathing  are  always 
working  the  chest  to  bring  fresh  air  into  the  lungs. 

36.  You  see  at  once  the  reason  why  such  muscles 
are  involuntary.     If  they  were  voluntary,  the  mind 
would  have  to  attend  to  them  all  the  time  to  keep 
them  at  work,  for  life  would  cease  if  the  respiration 
and  the  circulation  stopped.     The  mind,  therefore, 
not  only  could  not  have  any  time  for  sleep,  but  it 
would  have  every  moment  occupied  with  keeping  the 
circulating,   breathing  and    digestive  machinery  in 
operation,  and  could  not  attend  to  any  thing  else. 
But  as  it  is,  all  this  machinery  keeps  at  work  continu- 

Wbat  is  the  difference  between  voluntary  and  involuntary  muscles  ? 
Give  examples  of  both  kinds.  What  is  their  difference  as  to  resting? 
Why  are  the  heart  and  the  muscles  of  respiration  involuntary? 


152  FIRST   BOOK    IN    PHYSIOLOGY. 

ally  without  any  superintendence  on  the  part  of  the 
mind,  except  the  attention  that  is  required  to  supply 
the  digestive  machinery  with  its  material,  the  food 
that  we  eat. 

37.  But   the   muscles   of   the   respiration   are   not 
wholly  involuntary.     Although  they  commonly  work 
without   the  mind's  superintendence,   the    mind  can 
regulate  their  action  to  some  extent.      W e  can,  for 
example,   breathe   quicker  or  deeper  than  usual  if 
we  wish  to  do  so.     But  though  the  mind  can  regulate 
the  action  of  the  breathing  muscles,  it  cannot  wholly 
control  it.     ISTo  one  can  stop  his  breathing,  as  he  can 
stop  walking,  by  simply  willing  that  it  shall  stop. 

38.  Now,  there  are  two  reasons  why  the  mind  has 
this  partial  control  over  the  muscles  of  respiration. 
The  first  is,  that  it  uses  them  in  certain  acts,  as  speak- 
ing, singing,  blowing,  &c.     Another  is,  that  the  mind 
needs  to  direct  in  their  use  when  the  lungs  are  in  any 
way  embarrassed.     So  long  as  there  is  no  difficulty, 
the  breathing  is  performed  by  the  muscles  involunta- 
rily, without  any  superintendence  from  the  mind.  So 
long  as  the  mind  feels  no  inconvenience  it  scarcely 
ever  spends  even  a  thought  upon  the  breathing.    But 
as  soon  as  there  is  embarrassment  there  is  a  disagree- 
able sensation — that  is,  the  mind  is  informed  of  the 
embarrassment  through  the  nerves.     It,  therefore,  at- 
tends now  to  the  breathing  machinery,  in  order  to 
have  the  breathing  performed  in  the  best  manner 
possible.     For  example,  when  a  man  is  suffering  with 

How  much  are  the  muscles  of  respiration  influenced  by  the  will  If 
What  two  reasons  are  there  for  this?  How  much  notice  does  the 
mind  take  of  the  working  of  the  machinery  of  respiration  ? 


THE    EYE.  153 


asthma,  the  mind  directs  the  use  of  the  muscles  of  the 
chest,  so  as  to  get  as  much  air  as  possible  into  the 
lungs.  But  when  the  asthma  is  gone,  the  mind  ceases 
to  superintend  these  muscles,  and  the  breathing  goes 
on  again  by  their  involuntary  action. 

39.  While  the  muscles  of  respiration  are  both 
voluntary  and  involuntary  in  their  action,  the  heart  is 
wholly  an  involuntary  muscle  or  set  of  muscles.  No 
one  can  make  his  heart  beat  more  quickly  or  more 
slowly  by  determining  that  it  shall.  He  may  do  it 
by  exercise,  or  by  thinking  of  exciting  subjects,  but 
he  cannot  do  it  by  any  direct  action  of  the  will. 


CHAPTER    X. 

THE  EYE. 

1.  THE  eye  is  one  of  the  principal  instruments  that 
the  mind  uses  in  getting  a  knowledge  of  the  world 
around  it.     Though  it  is  a  small  organ,  it  is  a  very 
complicated  set  of   machinery.     It  has  many  struc- 
tures in  it  differing  much  from  each  other,  as  you  will 
see  as  I.  proceed.     It  has  six  nerves,  as  I  have  before 
told  you,  and  four  of  these  are  the  nerves  by  which 
the  mind  works  the  muscular  machinery  of  this  organ. 

2.  You  will  see,  in  this  chapter,  that  the  eye  is 
an  optical  instrument.     It  is,   therefore,  constructed 
somewhat  like  the  optical  instruments  that  man  makes, 

Is  the  heart  in  any  measure  a  voluntary  muscle  ?     What  is  said  of 
the  structure  of  the  eye  ?     What  kind  of  instrument  is  it  I     "What  in- 
struments is  it  like  ? 
7* 


164  FIRST   BOOK   IN    PHYSIOLOGY. 

but  is  much  more  perfect.  For  example,  it  is  like  a 
telescope,  and  it  is  also  like  a  camera-obscura.  And 
I  shall  show  you,  that  in  some  respects  it  is  like  the 
instrument  used  in  taking  daguerreotypes. 

3.  The  eye  is  contained  in    a  deep  bony  socket, 
which  you  see  in  Fig.  41,  on  page  111.     As  you  look 
at  the  eye  you  see  only  its  front,  with  a  portion  of  its 
sides,  as  it  rolls  in  its  socket.     It  is  in  shape  like  a 
globe,  but  it  is  not  perfectly  round.     Its  front  part, 
where  the  clear  window  is,  stands  out  a  little.     The 
eye  has  a  complete  case  enclosing  all  its  soft  and  deli- 
cate parts.     But  this  case  is  not  all  alike.     It  has  two 
parts  which  are  very  different  from  each  other.  There 
is  a  thick  white  part  called  the  sclerotic  coat,  from  a 
Greek  word,  meaning  hard.     It  is  what  is  commonly 
called  the  white  of  the  eye.     It  is  this  coat  that  gives 
the  firm  feeling  to  the  eye  when  you  press  your  finger 
upon  it.     But  this  coat  does  not  extend  over  the  front 
of  the  eye.     There  is  there,  as  you  see,  a  clear  trans- 
parent part  of  altogether  a  different  structure.     This 
fits  into  the  white  coat  very  much  as  a  watch-glass  fits 
into  the  case.     It  is  called  the  cornea. 

4.  Looking  through  this  window  of  the  eye,  you  see 
a  little  behind  it  a  delicate  colored  curtain,  called  the 
iris,  with  a  round  opening  in  it  called  the  pupil.    The 
iris  is  differently  colored  in  different  persons.     And 
we  call  the  eye  blue  or  brown  or  gray,  &c.,  according 
to  the  color  of  this  curtain.     Through  the  pupil  we 
look  into  the  very  inner  chamber  of  the  eye.     This 

What  is  the  situation  of  the  eye  ?  What  is  its  shape?  What  is  the 
sclerotic  coat  ?  What  is  the  cornea  ?  How  does  it  fit  into  the  sclerotic 
coat  ?  What  is  the  iris  ?  What  is  the  pupil  of  the  eye !  Into  what  do 
we  look  through  the  pupil  ? 


THE   EYE.  155 


always  has  a  dark  appearance,  because,  as  you  will 
soon  see,  this  chamber  has  a  lining  of  a  dark  color. 

5.  The  iris  makes  the  eye  very  beautiful.     But  it  is 
not  a  mere  ornament.     It  is  an  important  part  of  the 
machinery  of  the  eye.     Its  chief  office  is  to  regulate 
the  quantity  of  light  that  goes  into  the  eye.     You  can 
see  how  this  is  done.     If  you  look  into  the  eye  of  any 
person  while  you  hold  a  light  at  some  distance,  you 
see  that  the  pupil  is  quite  wide  open.     Now  bring 
the  light  near  the  eye,  and  you  will  see  the  pupil  in- 
stantly grow  smaller.     This  is  because  the  iris  or  cur- 
tain has  contracted  its  opening  in  order  to  keep  too 
much  light  from  going  into  the  eye.     In  the  glare  of 
a  bright  sun  this  opening  that  lets  in  the  light  becomes 
very  small ;  but  in  the  dark  it  is  very  wide  open,  be- 
cause the  eye  then  needs  all  the  light  that  it  can  get. 

6.  I  will  now  explain  the  way  in  which  the  iris 
acts  in  regulating  the  quantity  of  light  that  enters  the 
eye.     The  iris  has  two  sets  of  fibres,  straight  and  cir- 
cular.    These  are  represented  in  Fig.  63.     In  a  the 
pupil  is  wide  open.     Here  the 

circular  fibres  are  relaxed,  and 
the  straight  ones  are  contract- 
ed. In  b  the  pupil  is  contract- 
ed. And  here  the  fibres  are 
just  the  reverse  of  what  they  are  in  a — the  straight 
ones  are  relaxed  and  the  circular  ones  are  contracted. 

7.  The  fibres  of  this  round  curtain  must  be  very 
nicely  arranged,  and  be  made  to  act  with  great  exact- 
ness ;  for  the  iris  is  always  perfectly  even  as  it  en- 

What  is  the  chief  use  of  the  iris  ?    How  would  you  show  its  use  ? 
Explain  the  manner  in  which  the  iris  acts. 


156  FIRST    BOOK   IN   PHYSIOLOGY. 

larges  or  contracts  its  opening,  and  there  are  never 
any  wrinkles  in  it.  If  any  person  should  attempt  to 
construct  a  curtain  after  this  form,  with  a  round  open- 
ing in  it,  he  could  not  in  any  way  fix  the  strings  by 
which  the  opening  would  be  made  smaller  or  larger, 
so  as  to  keep  the  curtain  always  smooth  and  its  edge 
always  regular. 

8.  I  will  now  give  you  a  more  full  and  particu- 
lar description  of  the  parts  of  the  eye.  In  Fig.  64 
you  have  a  map  of  the  eye.  It  has  three  coats,  as 

FIG.  64. 


I 

they  are  called.  At  a  is  the  thick,  strong,  white 
coat,  the  sderotica.  Into  it  the  cornea,  e,  the  clear 
window  of  the  eye,  fits,  as  I  have  before  told  you, 
like  a  crystal  of  a  watch  in  the  case.  These  two 
parts,  the  cornea  and  the  sclerotica,  really  together 
make  one  coat.  Inside  of  the  sclerotic  coat  is  the 
cJwroid  coat,  I.  This  is  of  a  dark  color.  Why 

What  is  said  of  the  regularity  of  action  of  the  iris?     Describe  the 
parts  of  the  eye  as  represented  in  Fig.  64. 


- 
THE    EYE.  157 


this  is  so  I  will  tell  you  in  another  place.  At  c  is  the 
retina.  This  is  very  thin,  and  is  chiefly  composed  of 
the  fibres  of  the  optic  nerve,  d,  that  enters  the  eye  at 
its  back  part. 

9.  The  eye  has  three  humors,  as  they  are  called. 
There  is  the  aqueous,  or  watery  humor,  f,  in  the  front 
part  of  the  eye  behind  the  cornea.     The  iris,  g  g,  is  in 
the  midst  of  this  humor.  -  It  divides  the  chamber  that 
contains  the  humor  into  two  parts.     The  part  of  the 
chamber  which  is  in  front  of  the  iris  is,  as  you  see, 
much  larger  than  that  whicli  is  behind  it.    At  h  is  the 
crystalline  humor,  or  lens,  as  it  is  more  often  called. 
This  lens  is  a  substance  like  hard  clear  jelly.     Then 
behind  this,  filling  up  all  the  space,  i,  is  the  vitreous, 
or  glassy  humor,  which  is  like  soft  jelly.     You  see 
that  it  is  this  vitreous  hmnor  that  fills  up  a  great  por- 
tion of  the  ball  of  the  eye. 

10.  The  object  of  all  this  apparatus  that  I  have  de- 
scribed is  to  have  images  of  objects  formed  upon  the 
retina,  c.     That  these  images  are  formed  there  can 
be  proved  by  an  experiment.     Take  an  ox's  eye,  and 
peel  off  carefully  the  thick  rind  at  the  back  part,  that 
is,  the  sclerotic  coat,  so  that  very  little  but  the  retina 
is  left.     If  now  you  hold  a  candle  before  it,  you  can 
see  the  image  of  the  candle  on  the  retina  at  the  back 
part  of  the  eye.     So,  if  you  place  it  in  a  hole  in  the 
window-shutter,  the  images  of  objects,  such  as  houses, 
trees.  &c.,  can  be  seen  pictured  on  the  retina. 

11.  This  picturing  upon  the  retina  takes  place  with 
every  object  that  we  see.     If  we  look  at  a  single  ob- 

What  is  the  object  of  the  apparatus  of  the  eye  ?    How  can  you  prove 
that  images  are  formed  on  the  retina  ? 


158  FIRST   BOOK   IN    PHYSIOLOGY, 

ject,  as  a  candle,  its  image  is  formed  distinctly  in  the 
back  part  of  the  eye.  And  so,  also,  if  we  look  at  a 
wide  prospect,  all  the  multitude  of  objects  that  we  see 
are  pictured  there  in  a  space  that  a  sixpence  would 
cover. 

12.  I  will  now  explain  to  you  in  what  way  these 
pictures  are  formed  upon  the  retina.     It  is  the  light 
that  forms  them.     The  rays  of  light  that  come  from 
the  sun  are  reflected  from  every  object  in  all  direc- 
tions.    And  when  you  see  an  object,  it  is  because 
these  rays  reflected  from  it  enter  your  eyes,  and  make 
its  image  in  them.     For  example,  when  you  see  a 
tree,  the  light  which  is  reflected  from  the  tree  passes 
into  the  window  of  the  eye,  and  pictures  out  a  tree  on 
the  retina. 

13.  In  this  formation  of  the  pictures  of  objects  on 
the  retina,  the  eye  is  like  the  instrument  called  the 
camera-obscura.     In  this  instrument  there  is  a  dark 
chamber  into  which  light  is  admitted  through  glasses 
in  a  tube.     The  light  that  thus  comes  in,  pictures  in 
the  dark  chamber  of  the  instrument  the  trees,  houses, 
and  other  objects  that  are  in  front  of  the  tube.     And 
as  you  look  into  this  chamber  through  an  opening, 
you  see  the  picture.      That  dark  chamber  in  the  eye, 
that  is  filled  with  the  vitreous  humor,  is  like  the  dark 
chamber  of  the  camera-obscura,  and  the  lenses  and 
humors   of  the  eye  serve  the  same  purpose   as  the 
glasses  in  the  tube  of  this  instrument  do. 

14.  In  this  formation  of  pictures  of  objects,  the  eye 
is  also  like  the  instrument  used  in  taking  daguerreo- 

In  what  way  are  the  images  of  objects  pictured  on   the  retina  ? 
Trace  the  resemblance  of  the  eye  to  the  camera-obscura. 


- 
TIIE   EYE.  159 


types.  When  your  daguerreotype  is  taken,  the  rays 
of  light  that  shine  upon  your  face  are  reflected  or 
thrown  off  from  it  into  that  round  window  that  you 
look  at  in  the  instrument.  These  rays  enter  through 
this  window  into  a  dark  chamber,  just  as  they  do  in 
the  camera-obscura,  or  in  the  eye,  and  picture  your 
image  on  a  plate  of  metal  there.  This  plate  of  metal 
is  to  this  instrument  what  the  retina  is  to  the  eye. 

15.  The    metallic   plate    in   the   daguerreotyping 
instrument  differs  from  the  retina  in  one  important 
respect.     The  image   made  on  the  retina  does  not 
remain,  but  that  which  is  formed  on  the  metal  does. 
The  surface  of  the  metal  is  prepared  in  such  a  way 
that  the  image  made  by  the  light  is  left  there.     It  is 
a  beautiful  idea  that  light  should  thus  be  the  pencil 
to  paint  your  picture.     And  yet,  whenever  any  one 
looks  upon  you,  the  light  paints  your  picture  in  his 
eyes  upon  the  retina,  just  as  it  does  upon  the  metallic 
plate   in    the   daguerreotyping   instrument.     Indeed, 
every  object  that  is  seen,  is  for  the  moment  daguerre- 
otyped  upon  the  retina.     And  as  you  look  at  object 
after  object,  there  is  a  constant  succession  of  pictures 
made  there. 

16.  The  eye  is  in  some  respects  like  a  telescope.    It 
has   lenses  like  this  instrument.     The  pro-     FIO.  03. 
jecting  cornea  in  front  acts  as  a  lens.     But 

the  principal  lens  of  the  eye  is  the  crystal- 
line lens,  which  is  represented  in  Fig.  65. 
The  rays  of  light  are  brought  nearer  together 

How  does  the  eye  resemble  the  daguerreotyping  instrument  ?  What 
is  the  difference  between  the  picture  on  the  retina  and  that  on  {he  plate 
of  metal  in  the  daguerreotyping  instrument?  How  is  the  eye  like  a 
telescope  ? 


160  FIRST    BOOK    IN    PHYSIOLOGY. 

by  the  lenses  of  the  eye,  just  as  they  are  by  the  lenses 
of  the  telescope. 

17.  The  lenses  and  humors  of  the  eye  must  be  very 
exactly  arranged,  in  order  that  the  sight  may  be  per- 
fect. They  must  be  so  arranged  that  the  images  of 
objects  shall  be  formed  distinctly  on  the  retina.  Now  in 
near-sighted  persons  the  lenses  and  humors  are  so  ar- 
ranged as  to  make  the  rays  that  form  the  images  come 
together  too  quickly,  before  they  reach  the  retina.  This 

FIG.  66. 


is  represented  in  Fig.  66.  The  result  is,  that  a  confu- 
sed instead  of  a  clear  image  is  formed  on  the  retina. 
If  the  retina"  could  be  brought  forward  to  where  the 
figure  of  the  cross  is  represented,  the  image  would  be 
clear.  The  common  remedy  for  the  near-sighted  is  a 
FIG.  67.  glass,  that  has  an  effect  upon  the  rays  of  light 
the  opposite  of  that  which  is  produced  by  the 
cornea  and  the  crystalline  lens — that  is,  a  glass 
which  separates  the  rays  instead  of  bringing 
them  nearer  together,  and  so  prevents  the  rays 
from  coming  together  in  the  eye  too  soon. 
Such  a  glass  is  called  a  concave  lens.  Its  two 
sides  are  hollowed  out  more  or  less,  as  represented  in 
Fig.  67.  The  crystalline  lens,  seen  in  Fig.  65,  is,  on 
the  other  hand,  a  convex  lens. 

What  is  said  of  the  arrangement  of  the  lenses  and  humors  of  the  eye  ? 
What  is  the  difficulty  in  the  near-sighted  ?     What  is  the  remedy  ? 


THE   EYE. 


18.  That  large  rear  chamber  of  the  eye,  where  the 
images  of  objects  are  pictured  on  the  retina,  I  have 
told  you,  is  a  dark  chamber.     It  is  made  so  by  a 
coloring  substance  which  is  in  the  choroid  coat.     If 
it  were  not  dark  our  vision  would  be  indistinct,  from 
the  glare  of  light  in  the  eye,  just  as  it  is  when  we  go 
into  a  room  where  the  walls  are  all  of  a  very  light 
color.     In  the  albino  there  is  none  of  this  coloring 
matter  in  the  choroid  coat,  and  therefore  he  cannot 
see  well  in  a  bright  light.     Some  animals,  that  use 
their  eyes  only  in  the  night,  have  none  of  this  dark 
matter  in  them,  because  it  is  only  needed  when  the 
bright  light  of  day  is  shining  into  the  eye. 

19.  I  have  thus  shown   you  how   the  images   of 
objects  that  we  see  are  pictured  in  the  retina.     But 
this  is  not  all  the  process  that  we  call  seeing.     There 
is  something  more  needed  besides  the  formation  of 
these  images,  in  order  to   have  the  mind    see   the 
objects.     ]S"ow  the  mind  does  not  look  into  the  dark 
chamber  where  the  images  are,  as  we  look  into  the 
chamber  of  the  camera-obscura.     The  mind  gets   a 
knowledge  of  the  images  in  a  different  way  from  this. 
It  gets  it  by  means  of  the  optic  nerve,  the  end  of  which 
spread  out  forms  the  retina.     The  images  pictured 
there  make  impressions  on  the  net-work  of  the  nerve, 
and  these  impressions  go  to  the  brain  by  this  nerve, 
and  the  mind  feels  them.     In  regard  to  the  use  of  the 
word  impression,  in  speaking  of  the  operation  of  the 


What  is  the  cause  of  the  darkness  of  the  large  rear  chamber  of  the 
<jye  ?  Why  is  it  made  dark  ?  How  is  it  in  the  albino  ?  How  is  it  in 
some  animals  ?  In  what  way  does  the  mind  get  its  knowledge  of  the 
images  made  on  the  retina  ? 


162  FIRST   BOOK   IN   PHYSIOLOGY. 

nerves,  I  refer  you  to  what  I  have  said  in  the  chapter 
on  the  nervous  system,  §  20. 

20.  The  eye  may  be  in  perfect  order,  so  that  the  ima- 
ges of  objects  may  be  pictured  accurately  in  its  dark 
chamber,  and  yet  there  may  be  no  seeing.     For  the 
nerve  may  not  be  able  to  pass  the  impressions  on  to  the 
brain.     A  tumor,  for  example,  may  press  on  it  so  that 
nothing  can  pass  through  its  little  tubes.     It  is  by 
means  of  the  nerves,  then,  that  the  mind  makes  use 
of  its  optical  instruments,  just  as  is  true  of  all  the 
other  apparatus  or  machinery  of  the  body. 

21.  There  is  one  thing  very  curious  in  regard  to  the 
pictures  formed   on   the    retina.     They   are   always 
inverted  or  upside  down.     If  you  look  at  a  man,  for 
example,  he  is  pictured  on  your  retina  with  his  head 
down.    And  so  of  every  object.    Accordingly,  in  Fig. 
66  the  image  of  the  cross  in  the  eye  is  represented 
upside  down.     But  although  the  images  of  objects 
are  thus  reversed  on  the  retina,  your  mind  sees  every- 
thing right-side  up.     How  this  is  we  know  not,  but  in 
some  way  the  matter  is  so  fixed  in  the  brain  or  the 
nerves,  that  the  right  impression  goes  to  the  mind. 

22.  Observe  another  thing.     There  are  two  eyes. 
Of  course  there  are  two  images  of  every  object  that 
you  see,  and  two  impressions  are  carried  by  the  two 
optic  nerves  to  the  brain.     And  yet  the  mind  receives 
but  one  impression,  and  so  sees  but  one  thing.     This 
is  because  the  two  eyes  are  alike,  and  work  alike.     If 
this  were  not  so,  there  would  be  confused  and  double 

What  is  said  in  regard  to  the  optic  nerve  as  being  necessary  to  see- 
ing ?  What  is  said  of  the  position  of  the  images  on  the  retina  ?  What 
is  said  of  the  fact  that  we  have  two  eyes  ? 


THE   EYE.  163 


vision.  If  the  eyes  were  not  alike  throughout,  the 
pictures  in  the  two  retinas  would  not  be  alike,  and 
two  different  impressions  would  be  sent  by  the  two 
nerves  to  the  brain,  and  then  you  would  always  see 
two  things  instead  of  one — two  faces,  two  trees,  two 
houses,  and  so  on.  So  also,  if  the  muscles  of  the  eyes 
did  not  work  alike  you  would  see  double.  For  this 
reason,  if  you  press  your  finger  on  the  side  of  one  eye, 
you  see  everything  double ;  for  you  keep  the  two 
eyes  from  moving  together  as  they  usually  do. 

23.  There  are  several  reasons  for  our  having  two  eyes 
or  optical  instruments  for  the  mind  to  use,  instead  of 
one.  You  could  not  look  in  so  many  directions  with  but 
one  eye.     You  do  not  use  both  eyes  together  all  the 
time,  but  you  use  one  or  both,  as  you  find  most  con- 
venient.    Then  again,  if  you  lose  one  eye  by  any 
accident,  you  have  another.    And  we  cannot  conceive 
of  any  way  of  placing  a  single  eye  in  the  face  so  as 
to  look  as  well  as  two  eyes  do. 

24.  The  eye  is  a  very  tender,  and  at  the  same  time 
a  very  important  organ.     It  is,  therefore,  very  care- 
fully  guarded   against   injury.      Observe,    how   the 
bones  jut  out  all  around  it ;  the  bone  of  the  fore- 
head, that  makes  the  projecting  roof  of  the  socket, 
the  cheek-bone,  and  the  bones  of  the  nose.     These 
parapets  of  bone  are  so  arranged  that  they  receive 
almost  all  the  blows  that  are  aimed  at  the  eye.     The 
eye  is  therefore  seldom  injured,  except  by  something 
thrust  straight  into  it,  so  as  to  avoid  these  jutting 

How  is  it,  that  with  two  eyes  our  vision  is  not  confused  or  double  ? 
"What  reasons  can  be  given  for  our  having  two  eyes?  How  are  the 
bones  about  the  eye  arranged  so  as  to  guard  it  ? 


164 


FIRST    BOOK    IN    PHYSIOLOGY. 


walls  around  it.  Then,  too,  the  eye  has  a  cushion  of 
fat,  and  does  not  lie  against  the  hard  bone  of  the 
socket.  Now,  if  the  eye  sees  a  blow  coming,  the 
muscle  that  makes  the  motion  of  winking  shuts  the 
lids,  and  pushes  the  eye  back  against  this  soft  cushion. 
This,  of  course,  not  only  covers  it  up,  but  sinks  it 
deeper  between  the  parapets  of  bone,  and  so  puts  it 
more  out  of  the  reach  of  the  blow. 

25.  The  eyelashes  serve  to  keep  light  things,  flying 
in  the  air,  from  entering  the  eye.  The  muscle  that 
so  quickly  shuts  the  eye-lids,  however,  does  more  at 
this  business  of  keeping  out  intruders.  The  eye- 
brows, besides  being  an  ornament,  are  of  some  use  as 
a  protection.  If  they  were  not  there,  the  perspiration 
on  the  forehead  would  continually  run  down  into  the 
eye,  and  would  irritate  and  inflame  it.  The  eye- 
brows are  the  eaves  of 
the  roof  of  the  eyes'  hab- 
itation, and  the  perspira- 
tion drops  from  them 
upon  the  cheek  below. 

26.  There  is  a  beauti- 
ful apparatus  for  moist- 
ening and  washing  the 
eye.  The  tear-gland, 
that  makes  the  wash  for 
the  eye,  is  situated  above 
the  eye,  a  little  toward 
its  outside,  as  repre- 


Fio.  63. 


Does  the  eye  lie  directly  against  the  bone  of  its  socket?  What  is 
done  when  the  eye  sees  a  blow  coming?  How  is  the  eye  protected  by 
the  eye-lashes ?  How  by  the  muscle  of  the  eye-lids?  How  by  the 
eye-brows  ? 


THE   EYE.  165 


sented  at  #,  in  Fig.  68.  The  tears  are  carried  from  this 
factory  by  little  ducts,  as  seen  at  £,  and  are  poured  over 
the  surface  of  the  eye.  They  serve  to  keep  the  eye  inoist, 
so  that  it  can  be  moved  about  in  its  socket  easily  by 
the  muscles.  They  also  serve  to  wash  out  substances 
that  get  into  the  eye,  and  when  they  are  needed  for 
this  purpose  the  tear-gland  makes  them  abundantly. 
Fishes  have  no  tear-gland,  for  the  water  in  which 
they  live  answers  the  purpose  of  tears  in  their  case. 
Neither  have  they  any  eye-lids,  as  they  are  not  expo- 
sed to  dust,  or  motes,  or  flying  insects,  as  animals  that 
live  in  the  air  are.  For  the  purpose  of  moistening 
the  eye,  the  tears  come  from  the  gland  in  a  small 
amount  all  the  time.  Of  course,  there  must  be  some 
contrivance  for  the  passing  off  of  the  tears,  or  they 
would  continually  run  over  the  edges  of  the  lids. 
The  contrivance  is  this.  If  you  will  look  at  the  edges 
of  the  eye-lids,  you  will  see  on  each,  near  the  end 
toward  the  nose,  a  very  little  opening.  Into  these 
openings,  seen  at  c  c,  in  the  Figure,  the  tears  go,  and 
pass  through  two  ducts  which  unite  in  one,  de.  This 
ends  in  the  nose.  This  sink-drain  of  the  eye,  as  we 
may  call  it,  is  continually  emptying  its  contents 
there. 

27.  Sometimes  this  drain  gets  stopped  up,  and  then 
the  tears  overflow  their  banks,  the  lids,  and  run  down 
the  cheeks.  When  one  weeps,  the  tear  factory  makes 


Describe  the  tear  apparatus  ?  What  two  purposes  do  the  tears  serve  ? 
Why  have  fishes  no  tear-glands  and  no  eye-lids  ?  Describe  the  drain 
by  which  the  tears  are  carried  off.  From  what  causes  may  the  tears 
overflow  the  lids  ? 


166  FIRST   BOOK    IN    PHYSIOLOGY. 

FIG.  69.  _  tears  so  fast  that  the  drain  cannot  take 
them  all  away,  and  there  is  an  overflow. 
There  is  a  curious  contrivance  for  carry- 
ing off  the  tears  when  the  eyes  are  closed 
in  sleep.  The  lids  close  in  such  a  way 
as  to  leave  a  three-cornered  canal  be- 
tween them  and  the  surface  of  the  eye- 
ball, as  represented  in  Fig.  69.  In  this 
diagram  the  line  1)  is  the  surface  of  the  front  of  the 
eye,  and  a  points  to  the  edges  of  the  two  lids.  The 
little  open  space  which  you  see  shows  you  the  form 
of  the  canal.  It  is  through  this  canal  that  the  tears 
flow,  all  the  time  that  we  are  asleep,  to  the  openings 
that  lead  into  the  sink-drain. 

28.  There  is  still  another  contrivance,  in  regard  to 
the  tears,  which  I  will  notice.     Along  on  the  edge  of 
each  lid,  among  the  roots  of  the  eye-lashes,  are  some 
little   glands  that  secrete   an    oily  substance.     This, 
besides  oiling  the  eyelashes,  serves  to  keep  the  tears 
in  the  eye.     It  makes  an  oily  line  all  along  the  edge 
of  the  lid  ;  and,  as  water  does  not  mix  with  oil,  the 
tears  will  not  pass  over  this  line  unless  they  are  more 
abundant  than  usual.     If  it  were  not  for  this  simple 
but  effectual   contrivance,  the  tears  would  be  con- 
stantly diffused  over  the  edges  of  the  lids,  and  the  lids 
would  therefore  be  all  the  time  wet.     This  would 
certainly  be  the  case  with  the  lower  ones. 

29.  Such  is  the  wonderful  apparatus  of  the  human 
eye.     It  would  be  interesting  now  to  show  you  how 

What  contrivance  is  there  for  carrying  off  the  tears  during  sleep  ? 
Mention  the  contrivance  for  keeping  the  tears  from  moistening  the  out- 
side of  the  eyelids. 


THE   EYE.  167 


the  eyes  of  different  kinds  of  animals  vary  from  the 
human  eye  in  their  arrangements.  I  will  speak, 
however,  only  of  the  compound  eyes  found  in  insects. 
They  are  made  up  of  many  eyes.  Thus  in  the  two 
eyes  of  the  common  fly  there  are  eight  thousand  little 
eyes,  as  the  microscope  shows  us.  In  some  insects 
they  amount  to  twenty  thousand.  Each  of  these  is  a 
tube,  at  the  bottom  of  which  an  image  can  be  formed, 
just  as  you  have  seen  that  there  is  on  the  retina  of  the 
human  eye.  Each  of  these  eight  thousand  eyes  in  the 
fly  sees  perfectly  of  itself,  having  its  own  nerve  of 
sight.  The  fly  therefore  can  see  in  various  directions, 
without  turning  its  head,  and  it  sometimes  uses  one 
part  of  this  extensive  optical  apparatus  and  some- 
times another,  according  to  the  direction  in  which  it 
wishes  to  look  or  the  number  of  things  it  wishes 
to  see. 

30.  It  has  been  found  by  the  microscope  that  the 
little  eye-tubes,  of  which  the  eyes  of  insects  are  made, 
are  not  always  of  the  same  shape.  In  some  they  are 
hexagonal  or  six-sided.  This  is  the  case  with  the  eye 
of  the  yellow  beetle,  or  May-bug.  A  magnified  view 
of  a  small  portion  of  the  surface  of  this  insect's  eye  is 
given  in  Fig.  TO.  In  some  butter-  FlG- 70- 

flies  the  little  eyes  are  of  a  square 
shape,  as  represented  in  Fig.  71. 
Why  there  should  be  this  differ- 
ence in  shape  we  know  not.  These 
compound  eyes  of  insects  are 

What  is  said  of  the  eyes  of  insects  I  How  many  eyes  has  the  com- 
mon fly  ?  How  many  have  some  other  insects  ?  Are  the  eyes  of  insects 
all  shaped  alike? 


168  FIRST    BOOK    IN   PHYSIOLOGY. 

among  the  most  wonderful  things  Fl°'_IL 

that  the  microscope  has  revealed  to 
us.  We  admire  the  skill  and  power 
of  the  Creator  as  we  look  at  the  con- 
struction of.  the  human  eye  ;  but  His  >fe|^^^ 
skill  and  power  appear  vastly  more  wonderful,  when 
wre  think  of  the  eye  of  a  mere  common  insect,  as  made 
up  of  thousands  of  optical  instruments,  each,  though 
so  minute,  being  more  perfect  than  any  instruments 
that  man  can  make. 


CHAPTER    XI. 

THE  EAR. 

1.  THE  mind  acquires  the  knowledge  of  sounds  by 
the  apparatus  of  hearing.      This   apparatus  is  very 
complicated,  and  some  of  it  is  exceedingly  delicate. 
Before  describing  it  I  will  say  something  of  sound,  in 
order  that  you  may  better  understand  the  operation  of 
this  apparatus. 

2.  Sound  is  caused  by  a  vibration  or  shaking  of 
some  substance.     You  can  perceive  this  vibration  in  a 
bell  if  you  touch  it  after  it  has  been  struck.     If  the 
bell  is  quite  large  you  can  see  as  well  as  feel  the 
vibration.  You  can  see  it  in  the  string  of  a  piano  or  a 
violin.     It  is  the  vibration  of  the  cords  in  the  larynx 
that  produces  the  sound  of  the  voice.     It  is  not  solid 
bodies  alone  that  produce  sound  by  their  vibration. 

Why  are  the  compound  eyes  of  insects  more  wonderful  than  the  hu- 
man eye  ?  How  is  sound  produced  ?  Give  examples  of  sound  made  by 
the  vibration  of  air  ? 


THE    EAR.  169 


It  is  often  produced  by  the  vibration  of  the  air.  This 
is  the  case  in  whistling.  In  the  flute  it  is  the  vibra- 
tion of  the  air  in  the  instrument  that  produces  the 
sound.  And  so  of  other  similar  instruments. 

3.  When  the  vibrations  are  equal,  the  sound  is  a 
musical  one.    But  when  they  are  irregular,  the  sound 
is  a  noise,  that  is,  a  confused  sound. 

4.  Sound  passes  through  the  air  by  vibrations.     It 
may  be  said  to  pass  by  waves  in  all  directions,  just  as 
waves  go  in  all  directions  on  the  surface  of  water 
when  a  stone  is  dropped  into  it.     And  as  these  waves 
in  the  water  lessen  as  they  extend  from  the  spot  where 
they  begin,  so  the  waves  of  sound  lessen  the  farther 
they  are  from  where  the  sound  is  produced.     That  is, 
the  sound  dies  away  in  the  distance,  as  it  is  expressed. 

5.  That  sound  is  transmitted  in  this  way  through 
the  air  can  be  proved  by  experiment.     If  a  bell  be 
set  to  ringing  under  the  glass  receiver  of  an  air-pump, 
as  you  pump  the  air  out  of  the  receiver,  the  sound  of 
the  bell  becomes  more  and  more  faint,  till  at  length 
you  cannot  hear  it  at  all.  The  reason  is,  that  the  vibra- 
tions of  the  air  lessen  as  the  air  itself  lessens  and  be- 
comes thin ;  and  when  the  air  is   all  pumped  out, 
there  are  no  vibrations  to  convey  the  sound  of  the 
bell.     So,  too,  sounds  made  on  the  top  of  a  very  high 
mountain  are  not  as  loud  as  when  made  in  the  valley 
below,  because  the  air  at  so  great  a  height  is  very 
thin. 


What  makes  the  difference  between  a  musical  sound  and  a  noise  ? 
How  does  sound  pass  through  the  air  ?     Give  the  comparison  in  regard 
to  the  diffusion  of  sound.     How  can   you   prove  that  sound   passes 
through  air  by  vibrations  ? 
8 


170  FIRST   BOOK   IN    PHYSIOLOGY. 

6.  Other  substances  besides  air  transmit  the  vibra- 
tions or  motions  of  sound.  If  you  put  your  head  un- 
der water,  and  let  some  one  strike  two  stones  together 
under  the  water  at  some  distance  from  you,  you  will 
hear  the  sound.  That  is,  the  vibration  will  come  to 
your  ear  through  the  water.  If  you  place  a  watch 
between  your  teeth,  you  hear  its  ticking  quite  as  dis- 
tinctly as  when  you  put  it  to  your  ear.  In  this  case 
the  vibration  goes  to  the  nerve  of  hearing  by  the  teeth 
and  the  bones,  and  does  not  go  round  by  the  air  into 
the  tube  of  the  ear. 

7.  The  vibration  of  sound  passes  more  readily 
through  solids  than  through  the  air.  If  you  put  your 
ear  upon  the  end  of  a  long  log  you  can  hear  the 
scratch  of  a  pin  made  at  the  other  end.  And  yet  you 
cannot  hear  it  through  the  air  at  the  distance  of  only 
a  few  feet.  A  deaf  gentleman,  as  he  rested  the  bowl 
of  his  long  pipe  upon  his  daughter's  piano,  found  that 
he  could  hear  the  music  much  more  distinctly  than  he 
could  through  the  air.  In  this  case  the  vibration 
went  through  the  pipe  to  the  teeth,  and  then  through 
the  bone  to  the  nerve  of  hearing. 

8.  The  vibrations  or  waves  of  sound  are  reflected 
by  objects  against  which  they  strike.  For  this  reason 
a  sound  can  be  heard  further  along  a  wall  than  in  an 
open  field.  If  one  speaks  in  an  open  field,  the  sound 
is  scattered  in  all  directions.  But  the  wall  keeps  it 
from  being  thus  scattered.  For  the  same  reason,  a 


Illustrate  the  fact  that  other  substances  besides  air  transmit  the  vi- 
brations of  sound,  What  is  said  of  the  transmission^  sound  through 
solids  compared  with  its  transmission  through  air  ?  Illustrate  in  vari- 
ous ways  the  reflection  of  sound. 


THE    EAR.  171 


speaker  can  be  better  heard  in  a  building  than  in  the 
open  air.  In  this  case  the  walls  shut  in  the  waves  of 
sound.  So,  also,  a  speaker  can  be  heard  better  when 
the  ceiling  is  low  than  when  it  is  very  high.  When 
the  ceiling  is  high  much  of  the  sound  of  the  voice  is 
lost  in  the  space  above.  In  a  speaking-tube,  even  a 
whisper  can  be  heard  at  a  great  distance,  because  the 
waves  of  sound  are  so  shut  in  by  the  tube. 

9.  In  hearing,  the  waves  of  sound  are  caught  by 
the  outer  ear,  as  it  is  called,  and  they  go  into  the  tube 
which  you  see  there.     The  purpose  of  this  outer  ear  is 
to  collect  these  vibrations  and  direct  them  into  this 
tube.     It  is  well  shaped  on  the  whole  for  this  purpose, 
but  the  ridges  and  prominences  that  you  see  on  it  do 
not  render  any   assistance   in   this   respect.       They 
merely  serve  to  make  the  ear  a  comely  organ.     Some 
animals  have  ears  which  answer  much  better  in  col- 
lecting the  waves  of  sound  than  the  ear  of  man  does, 
because   they  need   them.      Man   could   hear  more 
easily  if  his  ears  were  larger,  and  were  shaped  more 
like  the  open  end  of  a  trumpet,  but  such  ill-looking 
appendages  are  not  necessary  in  his  case.     He  some- 
times assists  the  ear  in  collecting  the  vibrations  of 
sound  by  putting  his  hand  up  behind  it.     Yery  deaf 
persons  often  use  an  ear-trumpet.  The  broad  trumpet- 
shaped  end  is  turned  towards  the  speaker,  so  as  to 
catch  the  waves  of  sound  and  direct  them  into  the 
tube  of  the  ear  by  the  pipe  of  the  instrument. 

10.  The  vibrations  of  sound  in  the  air,  entering  the 

"What  is  the  purpose  of  the  outer  ear  ?  What  is  said  of  its  shape, 
and  the  irregularities  on  its  surface  ?  What  is  said  of  the  ears  of  some 
animals  ?  In  what  way  is  the  ear  sometimes  assisted  ? 


172  FIRST   BOOK   IN   PHYSIOLOGY. 

tube  of  the  ear,  strike  upon  a  drum  at  the  end  of  the 
tube.  This  drum  of  the  ear  is  a  membrane  fastened 
to  the  bone,  just  as  the  drum-head  of  a  common  drum 
is  fastened  to  its  wooden  rim.  The  vibrations  that 
thus  enter  this  tube  as  they  strike  the  drum  make  it 
to  vibrate. 

11.  The  vibration  does  not  stop  here.     It  is  commu- 
nicated to  a  chain  of  little  bones  on  the  other  side  of 
the  drum.     The  farther  one  of  this  chain  of  bones 
rests  on  another  membrane  or  drum.     The  vibration 
is  therefore  communicated  to  this  second  drum.    And 
this  drum  covers  an  opening  into  some  winding  pas- 
sages in  solid  bone.     These  passages  are  filled  with  a 
fluid,  and  the  vibration  of  the  drum  over  the  opening 
makes  this  fluid  to  vibrate  or  shake. 

12.  The  fine  delicate  fibres  of  the  nerve  of  hearing 
are  in  the  midst  of  the  fluid  in  the  winding  passages. 
They  feel  the  vibration  of  the  fluid  there,  and  an  im- 
pression goes  by  them  through  the  trunk  of  the  nerve 
to  the  brain,  and  is  received  there  by  the  mind.    And 
this  completes  the  process  of  hearing.     These  winding 
passages,  where  the  nervous  fibres  are  at  their  post 
ready  to  feel  the  vibrations  that  come  there,  are  the 
real  halls  of  audience,  as  we  may  call  them.     I  will 
now  describe  some  of  these  parts  more  particularly. 

13.  The  little  bones  in  the  ear  are  four  in  number. 
They   are   connected   together,   and   are    commonly 
spoken  of  as  a  chain  of  bones.    In  Fig.  72  they  are  re- 

Upon  what  do  the  waves  of  sound  entering  the  ear  strike  ?  Trace 
the  transmission  of  the  vibration  inward  from  the  drum  of  the  ear. 
Where  are  the  fibres  of  the  nerve  of  hearing,  and  how  are  they  affected  ? 
What  completes  the  process  of  hearing  ? 


THE   EAR. 


173 


presented  separate  and  considerably  magnified,  so  that 
you  can  see  their  shape  distinctly.  They  are  named 
from  their  shapes.  They  are  the  hammer,  m;  the 
anvil,  i  /  the  round  bone,  o,  the  smallest  bone  in  the 
body  ;  and  the  stirrup,  s.  The  Flo.  72. 

long  handle  of  the  hammer, 
h,  is  fastened  to  the  middle  of 
the  drum  of  the  ear,  and  its 
blunt  end  fits  on  to  the  anvil. 
The  little  round  bone  is  fixed 
between  the  slender  end  of 
the  anvil  and  the  top  of  the  stirrup.  And  the  bottom 
of  the  stirrup  presses  upon  the  second  drum  of  the 
ear.  In  Fig.  73  you  have  a  repre-  FIG.  73. 
sentation  of  these  bones,  together  with 
the  drum  of  the  ear.  When  the  vibra- 
tion of  sound  comes  to  these  bones, 
the  hammer  receives  it  first  and  it 
passes  to  the  anvil,  then  to  the  little 
round  bone,  then  to  the  stirrup,  which  communicates 
to  the  drum  that  is  over  the  opening  to  the  winding 
passages. 

14.  In  Fig.  73  is  represented,  much  magnified,  the 
shape  of  the  winding  passages,  which  I  have  told  you 
are  in  solid  bone.  The  middle  part  of  it,  v,  is  the 
vestibule,  or  common  hall  of  entrance  to  the  passages. 
From  this  go  out  on  the  upper  side  the  semi-circular 
canals,  x,  y,  z,  and  on  the  lower  side  the  passages  of 
the  cochlea,  k.  At  o  is  the  opening  into  the  vestibule 


Describe  the  little  bones  of  the  ear.     In  what  order  does  the  vibra- 
tion of  a  sound  pass  through  this  chain  of  bones  ?     Describe  the  winding 


174 


FIRST    BOOK    IN    PHYSIOLOGY. 


FIG 


that  is  covered  by  the  se- 
cond drum.  This  drum,  you 
will  remember,  is  pressed 
upon  by  the  stirrup-bone. 
-At  r  is  another  opening, 
which  is  also  covered  by  a 
membrane  or  drum.  The 
cochlea  is  called  so  because 
it  is  shaped  like  a  snail's 
shell.  It  is  most  curiously 
arranged,  having  two  spi- 
ral passages,  each  taking 
two  turns  and  a  half  around 
a  pillar  in  the  middle.  This  part  of  the  ear  represented 
iii  this  figure  is  called  the  labyrinth,  because  the 
winding  passages  are  so  complicated. 

15.  Having  thus  noticed  the  different  parts  of  the 
apparatus  of  hearing,  let  us  look  at  it  altogether,  as 
represented  in  a  map  of  it  in  Fig.  75.  At  a  1)  c  is  the 
external  ear ;  at  d  is  the  entrance  to  the  tube  of  the 
ear/;  at  g  is  the  drum  of  the  ear.  At  h  is  the  cavity 
beyond  the  drum  where  the  chain  of  bones  is,  the 
bones  being  left  out  that  the  arrangement  of  the  appa- 
ratus may  be  more  clear  to  you.  At  Jc  is  a  tube 
which  comes  from  the  back  part  of  the  throat  to  this 
cavity.  If  you  shut  your  mouth  and  close  the  nostrils 
with  your  fingers,  and  then  force  the  air  strongly 
from  your  chest  into  the  mouth,  you  can  feel  the  air 
pass  through  this  tube  into  the  ear  where  the  little 
bones  are.  At  I  is  the  vestibule  of  the  labyrinth  ;  at 

Why  are  the  winding  passages  called  the  labyrinth  ?  Describe  the 
various  parts  of  the  ear  as  represented  in  Fig.  75. 


THE    EAR. 


175 


FIG.  75. 


71 


m  are  the  semi-circular  canals ;  at  n  is  the  cochlea ; 
at  o  is  the  trunk  of  the  nerve  of  hearing  as  it  goes  to 
branch  out  in  the  labyrinth ;  and  at  e  e  is  the  bone  in 
which  the  labyrinth  is  inclosed. 

16.  I  will  now  describe  to  you  the  process  of  hear- 
ing, tracing  its  successive  steps  by  means  of  the  map 
of  the  apparatus.  The  vibrations  or  waves  of  sound 
go  into  the  tube  of  the  ear,  df>  and  strike  on  the  drum, 
<7,  making  it  to  vibrate.  This  vibration  is  communi- 
cated to  the  chain  of  bones  in  the  cavity,  h.  The 
last  bone  in  vibrating  shakes  the  little  drum  that  co- 
vers the  opening  into  the  winding  passages,  I  in  n. 
This  sends  a  vibration  throughout  the  fluid  in  all  these 

Trace  the  process  of  hearing  in  its  successive  steps  on  this  map  of 
the  apparatus. 


176  FIRST   BOOK    IN    PHYSIOLOGY. 

passages.  The  nervous  fibres  scattered  through  this 
fluid  feel  the  vibration,  and  the  trunk  of  the  nerve,  o, 
passes  on  the  impression  to  the  mind  in  the  brain. 

17.  Observe  that  there  are  five  different  vibrations 
in  succession  before  the  nerve  of  the  ear  is  reached — 
the  vibration  of  the  air,  in  the  tube  of  the  ear,  / — of 
the  drum,  g — of  the  chain  of  bones  in  the  cavity,  h — 
of  the  little  drum  over  the  opening  into  the  winding 
passages — and  lastly,  of  the  fluid  in  these  passages. 
Every  time  that  a  sound  is  heard,  these  vibrations  fol- 
low each  other,  in  the  order  that  I  have  mentioned. 
It  seems  a  long  process,  as  it  is  described,  but  it  takes 
but  an  instant.     And  in  hearing  one  speak,  how  rap- 
idly does  one  vibration  follow  another,  and  yet  how 
distinct  the  different  vibrations  are  as  one  sound  suc- 
ceeds  another.     The    successive   vibrations   can    be 
exceedingly  rapid,  and  yet  be  entirely  distinct.     You 
can  observe  this  in  the  rapid  strokes  of  some  kinds  of 
machinery.     You  can  observe  it  also,  as  you  strike  as 
rapidly  as  you  can  with  a  stick  upon  anything.     For 
every  blow  of  the  stick  you  have  the  succession  of 
vibrations  that  I  spoke  of  in  the  first  part  of  this  par- 
agraph.    And  you  cannot  strike  fast  enough  to  make 
the  vibrations  mingle  together. 

18.  I  have   described    hearing   as  it    commonly 
occurs.     But,  as  I  have  already  told  you  in  §  6,  sounds 
do  not   always  go  in  through  the  tube  of  the  ear. 
They   sometimes  get    to    the   winding  passages   by 
another  way;  as  for  example,  the  sound  of  the  watch 

How  many  different  vibrations  are  there  for  every  sound  ?  What  is 
said  of  the  distinctness  and  rapidity  of  the  vibrations  as  they  follow 
each  other  ? 


THE  EAR.  177 


when  placed  between  the  teeth.  In  such  a  case,  there 
are  not  so  many  changes  in  the  vibration  as  when  we 
hear  in  the  common  way.  There  are  only  three 
vibrations  to  follow  each  other  for  every  sound,  viz., 
the  vibration  of  the  teeth,  that  of  the  bones  between 
the  teeth  and  the  winding  passages  of  the  ear,  and 
that  of  the  fluid  in  these  passages. 

19.  You  see,  then,  by  such  cases  that  there  can  be 
hearing  without  using  the  drum  of  the  ear  or  the 
chain  of  bones.    Indeed  these  parts  may  be  destroyed, 
and  yet  if  the  winding  passages  are  not  at  all  injured, 
the  person  can  hear,  though  of  course  hot  as  well  as 
when  the  apparatus  is  all  there.     The  winding  pas- 
sages, the  halls  of  audience,  as  I  have  called  them,  are 
then  really  the  essential  part  of  the  apparatus.     And 
so  long  as  the  vibration  of  sound  can  in  any  way  reach 
the  fluid  in  them,  and  shake  it  so  that  the  fibres  of  the 
nerve  shall  feel  it,  there  will  be  hearing.     But  if  the 
fluid  be  in  any  way  let  out  of  these  passages  there 
will  be  no  hearing,  although  the  drum  of  the  ear  and 
the  chain  of  bones  may  be  in  perfect  order,  and  may 
vibrate  regularly  to  the  sounds  that  come  into  the 
tube  of  the  ear.     The  vibration  in  this  case  will  stop 
at  the  stirrup-bone,  and  will  not  reach  the  nerve. 

20.  This  innermost  and  most  important  part  of  the 
apparatus  is  very  securely  guarded  from  injury.    The 
winding  passages  are  inclosed  in  the  hardest  bone  in 
the  body.     It  is  so  hard  that  it  is  called  the  petrous 
or  rock-like  bone. 


May  sounds  be  beard  in  some  otber  way  tban  tbrougb  tbe  tube  of 
the  ear  ?  What  is  the  most  important  part  of  the  apparatus  of  hearing  ? 
Explain  in  full.  How  are  tbe  winding  passages  guarded  from  injury  ? 

8* 


178  FIRST   BOOK   IN   PHYSIOLOGY. 

21.  The  outer  passage  into  the  ear  is  well  guarded, 
and  in  rather  a  singular  way.     Besides  the  hairs  that 
are  in  the  tube,  which  serve  to  catch  particles  that 
may  fly  in,  there  is  also  a  waxy  substance  secreted 
there.     And  this  substance,  though  it  is  so  different 
from  anything  else  in  the  body,  is,  like  everything 
else,  made  from  the  blood.     It  is  made  by  some  very 
small  glands  situated  in  the  lining  of  the  tube.     It  is 
very  bitter,  and  the  odor  of  it  serves  to  keep  out  small 
insects  which  might  otherwise   creep   or  fly  in.     It 
answers  this  purpose  so  well,  that  although  the  tube 
is.  always  open,  it  is  quite  uncommon  to  have  an  insect 
get  into  the  ear.     And  when  one  does,  it  becomes  so 
enveloped  in  the  wax  that  its  struggles  can  do  but  lit- 
tle harm.     Commonly  the  insect  soon  dies — perhaps, 
in  part,  from  the  bitter  dose  which  he  is  obliged  to 
take. 

22.  I  have  thus,  in  this  and  the  previous  chapter, 
treated  quite  fully  of  two  of  the  senses.     Of  the  other 
senses  I  have  spoken  incidentally  in  other  parts  of  the 
book.     The  organs  of  the  different  senses  differ  from 
each  other,  as  they  are  fitted  to  inform  the  mind  of 
the  different  qualities  of  things  around  it.    For  exam- 
ple,  the  organ  of  smell  is  very  different  from  the 
organ  of  hearing.     Fine  particles  pass  from  bodies 
that  give  out  an  odor ;  and  these,  coming  in  contact 
with  the  nerve  spread  out  in  the  nose,  make  an  im- 
pression, which  is  transmitted  by  the  nerve  to-  the 
brain.     But  in  hearing,  no  particles  from  the  sound- 
ing body  come  in  contact  with  the  nerve.     A  mere 
shaking  or  vibration  goes  through  the  air  to  the  drum 

How  is  the  tube  of  the  ear  guarded  ?     Give  the  difference  stated 
between  the  organ  of  smell  and  that  of  hearing  ? 


THE   EAR.  179 


of  the  ear,  and  is  passed  on  from  this  through  the 
chain  of  bones  to  the  fluid  that  surrounds  the  fibres 
of  the  nerve  of  hearing. 

23.  In  the  sense  of  taste,  the  particles  of  the  sub- 
stance tasted  are  commonly  applied  in  a  coarser  way 
to  the  nerve  than  in  the  sense  of  smell.     In  the  sense 
of  touch,  the  substances  do  not,  as  in  smell  and  taste, 
come  into  actual  contact  with  the  nerves.     They  are 
felt  through  the  cuticle  ;  for  this,  as  I  have  told  you 
in  §  28,  Chapter  YL,  is  not  sensitive  at  all ;  that  is, 
it  has  no  nerves,  but  is  only  a  soft  delicate  covering 
to  the  very  sensitive  true-skin. 

24.  In  regard  to  the  sense  of  sight,  we  know  not 
what  it  is  that  enters  the  eye  and  pictures  the  images 
of  things  on  the  retina.     Light  is  now  generally  sup- 
posed to  be  a^  vibration  of  an  exceedingly  fine  sub- 
stance, finer  than  air,  which  is  thought  to  exist  every- 
where.    The  vibration  of  this  substance,  which  is 
called  ether,  is  thought  to  be  like  the  vibration  of  air 
in  sound.     Like  that,  it  goes  in  waves,  in  all  direc- 
tions, from  where  it  begins.     If  light  and  sound  are 
thus  only  motions,   they  are  in  some  respects  dif- 
ferent  motions.     They   never    interfere   with    each 
other,  though  they  are  continually  mingled  together, 
and  cross  each  other  in  all  directions.     They  differ  in 
one  respect  very  much.    Light  is  a  much  faster  vibra- 
tion than  sound.     If  you  look  at  a  cannon  fired  at  a 
distance,  the  flash  comes  to  your  eye  much  sooner  than 
the  sound  comes  to  your  ear.     The  same  is  true  also 
"of  the  flash  of  lightning  and  its  sound,  the  thunder. 

What  is  said  of  the  sense  of  taste?  What  of  the  sense  of  touch? 
What  is  light  supposed  to  be?  What  is  said  of  the  vibrations  of  light 
and  sound  ? 


180  FIRST    BOOK   IN    PHYSIOLOGY. 

CHAPTER    XII. 
CONNECTION  OF  THE  MIND  AND  BODY. 

I  HAVE  already  said  much  of  the  connection  of  the 
mind  and  the  body.  I  showed  you  in  the  chapter  on 
the  Nervous  System  that  this  connection  is  main- 
tained by  means  of  the  brain  and  the  nerves.  You 
there  learned,  that  all  the  knowledge  which  the  mind 
gets  of  the  world  around  it  comes  from  the  senses  by 
means  of  the  nerves ;  and  also  that  the  only  way  in 
which  the  mind  communicates  its  knowledge  to  others 
is  by  means  of  the  nerves  that  excite  the  muscles  to 
action.  In  the  chapters  following  that  on  the  Ner- 
vous System,  we  considered  the  instruments  by  which 
the  brain  and  nerves  operate  in  thus  connecting  the 
mind  with  the  world  around  it.  These  instruments 
are  the  muscles  and  bones,  and  the  organs  of  the 
senses,  the  eye,  the  ear,  the  nose,  the  mouth,  and  the 
skin.  In  this  chapter  I  wish  to  carry  you  on  a  little 
farther,  and  show  you  more  than  I  have  yet  done  in 
regard  to  the  manner  in  which  the  mind  uses  these 
instruments  by  means  of  the  nerves. 

2.  The  mind  is  connected  with  every  part  of  the 
body.  It  therefore  feels  what  is  done  to  any  part, 
and  it  can  move  the  muscles  everywhere  by  willing  to 
have  them  moved.  But  the  mind,  though  it  is  con- 
nected with  every  part,  is  not  in  every  part.  If  you 
pinch  your  finger  the  mind  feels  it  as  readily  as  if  it 

Give  the  summary,  in  §1,  of  what  has  been  already  said  in  regard  to 
the  connection  of  the  mind  and  the  body.  How  do  you  know  that  the 
mind  is  connected  with  every  part  of  the  body  ? 


CONNECTION   OF   THE   MIND   AND   BODY.     181 

were  itself  in  the  finger.  So,  also,  it  can  move  the 
finger  as  easily  as  if  it  were  really  there  among  the 
muscles.  But  if  the  hand  be  palsied,  feeling  and  mo- 
tion are  gone  in  the  part ;  and  yet  the  mind  may  be 
active,  and  move  other  parts  that  are  not  palsied,  and 
feel  what  is  done  to  them. 

3.  The  mind,  then,  is  not,  as  life  is,  all  over  the 
body.     It  is  in  the  brain.     This  is  its  central  office, 
the  nerves  being  its  communicating  wires.     We  seem 
to  know  very  early  in  life  that  the  mind  is  in  the 
brain.     The  child  is  conscious  that  he  does  his  think- 
ing in  his  head.     But  besides  this  consciousness,  we 
know  some  facts  that  prove  that  the  mind  resides  in 
the  brain.     Thus,  if  a  man  be  knocked  down  senseless 
by  a  blow  on  his  head,  the  mind  feels  nothing,  and 
can  move  no  part,  because  the  mind's  organ,  the  brain, 
is  so  much  affected  by  the  blow.     He  breathes  still, 
and  his  heart  beats,  because  the  mind,  as  you  saw  in 
§  33  in  the  chapter  on  the  Muscles,  does  not  control 
these  operations.    If  the  blow  break  the  skull,  and  the 
broken  part  be  pressed  in  upon  the  brain,  the  man 
will  not  think,  and  feel,  and  move,  until  the  surgeon 
remove  the  pressure  by  raising  the  broken  piece. 

4.  The  brain  is  shown  to  be  the  organ  of  the  mind 
by  the  manner  in  which  the  mind  is  affected  by  dis- 
ease in  the  brain.  Fever  causes  delirium  by  disordering 
the  brain,  and  a  violent  inflammation  of  the  brain  pro- 
duces fierce  delirium.     We  sometimes  see  the  mind 
blotted  out,  step  by  step,  by  slow  disease  in  the  brain, 

How  do  you  know  that  the  mind  is  not  in  every  part  ?  "What  is  said 
of  the  consciousness  that  the  mind  has  its  seat  in  the  brain?  "What 
fact  can  you  cite  that  proves  that  it  has  its  seat  there  ? 


182  FIRST   BOOK    IN   PHYSIOLOGY. 

so  that  the  strong-minded  man  becomes  gradually  like 
an  idiot. 

5.  You  see,  then,  that  the  mind  or  soul,  so  long  as 
it  remains  in  the  body,  is  dependent  upon  the  brain. 
It  can  act  only  ~by  means  of  this  organ.    If  the  brain 
be  disordered  in  any  way,  the  mind  acts  in  a  disordered 
manner.      If  the  brain  be  much  pressed  upon,  the 
mind  cannot  think,  nor  feel,  nor  move  any  part  of  the 
body.     The  mind  is  still  there,  but  it  is  torpid.  When 
the  pressure  is  taken  off,  it  comes  out  of  this  torpid 
state. 

6.  As  the  brain  is  the  organ  with  which  the  think- 
ing is  done,  we  find  that  those  animals  that  think 
much  have  larger  brains  than  those  that  think  but  lit- 
tle.    A  frog  thinks  very  little,  and  he  has  a  small 
brain.     An  oyster  thinks  still  less,  and  it  would  be 
hard  to  make  out  where  his  brain  is.     But  such  ani- 
mals as  the  canary-bird,  the  dog,  and  the  horse,  that 
know  so  much,  have  brains  of  considerable  size.   Man 
has  a  larger  brain  in  proportion  to  his  body  than  any 
other  animal,  because  he  has  to  think  so  much  more 
than  other  animals  do.     And  men  that  think  much 
have  larger  brains  than  the  stupid  and  ignorant. 

7.  The  mind  in  the  infant  is  feeble,  just  like  its 
body.     It  knows  but  little.     But  as  the  body  grows, 
the  mind  grows  also,  and  continually  adds  to  its  know- 
ledge.    I  wish  to  show  you  now  how  it  does  this. 

8.  If  you  look  at   a  very  young  infant,  you  will 
see  that  it  does  not  know  as  yet  how  to  use  its  mus- 
cles at  all  well.     It  moves  its  hands  about  awkwardly. 

How  does  disease  sometimes  show  that  the  miud  resides  iu  the  brain  ? 
What  is  said  of  the  size  of  the  brain  iu  different  animals  and  iu  man  ? 
What  is  sai  j  of  the  mind  of  the  infant  ? 


CONNECTION   OF   THE   MIND   AND    BODY.    183 

It  cannot  even  hold  any  thing  in  them.  It  does 
not  use  its  eyes  well.  It  cannot  turn  them  so  as  to 
look  directly  at  any  thing,  but  they  roll  about  in 
their  sockets  irregularly.  It  does  not  see  any  thing 
clearly. 

9.  The  mind,  you  see,  then,  has  to  learn  to  use  its 
instruments,  the  senses  and  the  muscles.      And  the 
more  it  learns  how  to  use  them,  the  more  knowledge 
it  gets  of  the  world  around  it.     It  learns,  for  example, 
to  use  the  muscles  and  the  nerves  of  touch,  so  as  to 
know  hard  things  from  soft,  rough  from  smooth,  &c. 
In  these  ways  it  is  continually  learning  more   and 
more  about  the  world  of  things  with  which  it  is  sur- 
rounded. 

10.  In  learning  to  use  the  senses,  the  mind  makes 
one  sense  help  another.     Thus,  the  child  sees  a  thing 
held  before  it,  but  as  he  reaches  out  his  hands  to  touch 
it,  it  is  plain  that  he  does  not  know  at  first  how  far  off 
it  is.     But  after  a  while,  by  touching  it  again  and 
again,  he  knows  where  it  is.     That  is,  by  his  sense  of 
touch  he  corrects  the  report  which  the  sense  of  sight 
makes  to  his  mind.    He  makes  many  such  corrections 
every  day,  and  after  awhile  becomes  able  generally  to 
estimate  at  what  distance  objects  are  the  moment  he 
looks  at  them.     Just  so  the  infant  has  to  learn  to  use 
its  ears  as  well  as  its  eyes.     It  knows  nothing  at  first 
of  the  direction  of  sound,  or  of  the   distance  from 
which  it  comes. 


is  said  of  the  use  which  the  infaot  makes  of  the  muscles  and 
the  senses  ?  What  is  said  of  its  learning  to  use  them  ?  Illustrate  the 
fact  that  the  mind  makes  one  sense  help  another  in  learning  to  use  the 


184  FIRST   BOOK   IN   PHYSIOLOGY. 

11.  It  is  a  long  training  that  the  mind  has  to  go 
through  in  learning  to  use  the  muscles.     The  hand  of 
the  infant  is  of  little  use  at  first,  but  after  a  time  he 
learns  to  hold  things  in  it.     And  from  this  the  mind 
goes  on  to  use  the  muscles  of  the  hand  more  and 
more,  till,  in  some  cases,  as  in  the  skilful  engraver  or 
penman,  it  acquires  wonderful  skill  in  the  movement 
of  these  muscles.     The  child  learns  to  perform  many 
different  motions  before  he  comes  to  try  that  very 
general  motion  of  the  muscles  of  the  body,  creeping. 
And  then,  in  learning  to  walk,  all  the  muscles  that 
move  the  body,  the  head,  the  legs  and  the  arms,  are 
exercised  in  balancing  movements,  day  after  day,  for 
a  long  time,  before  he  can  acquire  such  skill  in  the 
use  of  the  muscles  as  to  walk  off  readily  and  with 
scarcely  thinking  of  what  he  is  doing. 

12.  In  learning  to  talk  and  sing,  the  mind  learns 
how  to  use  muscles,  just  as  in  learning  to  walk.  These 
are  nicer  and  more  difficult  operations,  and  so  it  takes 
the  mind  longer  to  learn  them  than  to  learn  to  use  the 
muscles  in  walking.     Especially  is  this  true  of  learn- 
ing to  sing.     The  mind  is  obliged  to  practice  a  long 
time  on  the  muscles  of  the  larynx,  in  order  to  use 
them  skilfully  in  singing. 

13.  In  training  the  muscles  of  the  voice  in  speaking 
and  in  singing,  the  ear  acts  as  the  teacher.    It  is  only 
by  the  hearing  that  we  know  that  we  make  the  right 
sounds.     When  the  child  begins  to  talk,  he  makes 
various  trials  of  the  sounds  that  he  wishes  to  utter,  his 

What  is  said  of  the  time  required  for  learning  to  use  the  muscles  ? 
What  is  said  of  learning  to  talk  and  sing  ?  Why  does  it  take  longer  to 
learn  to  do  these  than  to  learn  to  walk  ? 


CONNECTION    OF  THE   MIND   AND   BODY.     185 

ear  all  the  time  listening,  that  his  mind  may  know 
when  he  utters  them  correctly.  So,  when  one  is  learn- 
ing to  sing,  the  ear  listens  to  inform  the  mind  when 
the  note  is  properly  sounded.  In  learning  both  to 
talk  and  sing,  the  ear  is  thus  continually  correcting 
the  mistakes  which  the  mind  makes  in  using  the  mus- 
cles of  the  voice. 

14.  So  necessary  is  the  ear  in  the  training  of  the 
muscles  of  the  voice,  that  these  muscles  are  never 
used  in  a  child  that  is  born  deaf.     In  almost  all  the 
deaf  and  dumb  there  is  no  defect  in  the  organs  of  the 
voice.     The  apparatus  is  all  there — the  articulating 
parts,  the  tongue,  palate,  &c.,  the  larynx  with  its  vocal 
ligaments,  and  the  muscles  that  tighten  them,  so  that 
they  may  vibrate,  and  the  muscles  of  the  chest  that 
force  out  the  air  to  strike  upon  them.     And  the  mind 
has  its  nerves  running  from  the  brain  to  all  parts  of 
the  apparatus.  But  the  mind  does  not  work  the  appara- 
tus, or  play  on  the  instrument,  as  we  may  say,  simply 
because  it  has  no  guide  in  doing  it.     There  being  no 
hearing,  the  mind  has  no  means  of  knowing  when  the 
right  sound  is  uttered,  and  therefore  it  utters  none. 
The  deaf  and  dumb  are  dumb  because  they  are  deaf. 

15.  If  a  child,  instead  of  being  born  deaf,  becomes 
deaf  while  it  is  learning  to  talk,  he  will  remember  the 
motions  of  the  muscles  of  the  voice  by  which  he 
uttered  some  words,  the  names  of  common  objects, 
such  as  hat,  watch,  &c.     He  can  therefore  pronounce 
these  words,  but  he  does  it  very  awkwardly,  because 
there  is  no  hearing  to  guide  the  voice. 

What  acts  as  the  teacher  in  learning  to  talk  and  sing  ?  Illustrate 
this.  What  is  said  of  the  deaf  and  dumb  ?  What  is  said  of  children 
that  become  deaf  and  dumb  while  learning  to  talk  ? 


186  FIRST   BOOK   IN   PHYSIOLOGY. 

16.  I  have  thus  told  you  how  the  mind  uses  the 
muscles  of  the  body.     It  is  a  very  complicated  ma- 
chinery that  the  mind  works.     There  are  over  four 
hundred  muscles  in  the  body,  and  the  mind  works 
them  by  a  multitude  of  nerves  that  go  from  the  brain 
to  them. 

17.  Observe,   now,   that  the  mind  in  most  cases 
knows  nothing  about  all  this  machinery  of  the  mus- 
cles.    Your  mind  wills  that  your  hand  be  raised,  and 
it  is  instantly  done.    You  may  not  know  what  muscles 
do  this,  and  if  you  do  you  cannot  perform  the  motion 
any  better  than  if  you  did  not  know.     The  anatomist 
that  knows  the  names  of  all  the  muscles,  and  under- 
stands how  they  are  arranged,  cannot  use  them  any 
better  than  those  who  know  nothing  about  this.     The 
skilful  balancer  would  not  be  any  more  skilful,  if  he 
had  all  the  knowledge  which  the  anatomist  has.    The 
famous  singer  could  not  sing  any  better  if  he  should 
know  how  the  little  muscles  in  his  throat  work  in  pro- 
ducing the  different  notes. 

13.  When  man  works  any  machinery  that  he  has 
made,  it  is  necessary  that  he  should  understand  its 
various  contrivances.  Thus,  the  sailor  cannot  guide 
the  ship  unless  he  knows  all  about  its  rigging.  But  it 
is  not  so,  as  you  have  seen,  with  the  machinery  that 
the  mind  works  in  the  body.  The  mind  does  not 
look  at  the  hundreds  of  muscles  that  it  works,  as  the 
sailor  looks  at  the  various  ropes  with  which  he  man- 


What  is  said  of  the  muscular  machinery  that  the  mind  works  ?  How 
much  does  the  mind  know  about  this  machinery  ?  Could  it  work  any 
better  if  it  knew  all  about  it  ?  State  the  comparison  given  in  regard  to 
machinery  made  by  man. 


CONNECTION   OF   THE   MIND   AND   BODY.    187 

ages  his  vessel.  And  when  it  wishes  to  perform  any 
motion,  it  is  not  obliged  to  consider  what  muscles  it 
must  put  into  action.  It  simply  wills  that  the  motion 
shall  be  done,  and  instantly  something,  we  know  not 
what,  goes  along  a  multitude  of  nerves  to  a  multitude 
of  muscular  fibres,  and  they  contract  just  enough  to 
perform  the  motion. 

19.  For  every  different  motion  a  different  message, 
as  we  may  call  it,  is  sent  along  the  nerves.     If  you 
raise  your  hand,  a  message  is  sent  through  the  nerves 
to  the  muscles  that  do  it.     Now,  if  you  raise  it  again, 
but  in  a  little  different  manner,   a  little   lower  or 
higher,  or  a  little  more  to  one  or  the  other  side,  a  lit- 
tle different  message  is  sent  along  the  nerves  to  those 
muscles.     And  the  same  can  be  said  of  the  muscles 
of  any  other  part  of  the  body.     You  see,  then,  that 
while  any  machinery  made  by  man  can  perform  but 
a  few  motions,  this  machinery  of  the   muscles   can 
perform  motions  of  any  variety. 

20.  I  have  already  spoken  of  the  variety  of  mo- 
tion that  the  muscular  machinery  can  perform^  in  the 
chapter  on  the  muscles,  §  12  and  §  13,  and  therefore 
will  not  dwell  on  it  here.     For  all  this  variety  there 
is  a  corresponding  variety  in  the  messages  or  impres- 
sions sent  from  the  mind  to  the  muscles.     Even  when 
the  muscles  only  vary  in  the  degree  of  their  action, 
for  every  different  degree  there  must  be  a  different 
message.     Thus,  if  in  playing  on  a  piano,  you  press 


said  of  the  different  motions  performed  by  muscles  ?  Illus- 
trate by  referring  to  the  hand.  What  is  said  of  the  great  variety  of 
muscular  action.  Illustrate  this  variety  as  produced  by  varying  the 
degree  and  the  direction  of  the  action  of  muscles? 


188  FIRST   BOOK  IN   PHYSIOLOGY, 

on  the  same  key  twice  in  the  same  way,  except  that 
you  vary  the  degree  of  pressure,  two  different  mes- 
sages are  sent  to  the  muscles  that  make  the  pressure, 
telling  them  in  each  case  how  hard  to  press.  Much 
more,  then,  must  the  messages  of  the  mind  to  the  mus- 
cles vary,  when  their  action  is  not  only  varied  in  de- 
gree, but  in  direction  also,  as  when  the  hand  moves 
from  one  key  to  another  in  playing  on  the  piano. 

21.  In  the  chapter  on  the  Muscles  you  saw  that 
generally  many  muscles  act   together  in  producing 
any  motion.     For  the  different  motions  of  any  part, 
then,  there  must  be  a  vast  variety  of  messages  sent 
along  the  nerves  of  the  muscles  in  that  part.  You  can 
get  some  idea  of  this  variety,  if  you  move  your  hand 
about  in  as  many  different  ways  as  you  can  think  of, 
remembering  what  a  number  of  muscles  there  is  at 
work  while  you  are  doing  this. 

22.  In  estimating  the  variety  of  the  messages  sent 
to  the  muscles,  you  are  to  remember  that  a  separate 
message  is  sent  to  every  fibre  of  a  muscle  by  its  little 
nervous  tube,  as  mentioned  in  §  9,  in  the  chapter  on 
the  Nervous  System.     How  wonderful  it  is,  that  in 
all  this  multitude  of  messages  that  are  sent  to  the 
fibres  of  the  muscles,  there  should  commonly  be  no 
mistake  in  any  of  them.     In  every  motion  each  fibre 
gets  its  message  correctly,  and  acts  in  obedience  to  it. 
You  will  realize  how  wonderful  this  is,  if  you  turn 
back  to  the  chapter  on  the  Muscles,  and  read  again 

What  is  said  in  §21  of  the  variety  of  messages  sent  by  the  nerves  to 
the  muscles  of  any  part  ?  What  are  you  to  remember  in  estimating 
this  variety  ?  What  is  very  wonderful  in  regard  to  this  ? 


CONNECTION   OF   THE   MIND   AND   BODY.    189 

all  that  I  say  there  of  the  variety  there  is  in  the  action 
of  the  muscles. 

23.  When  the  muscles  in  different  parts  of  the 
body  are  at  work  at  the  same  time,  in  some  general 
movement,  the  variety  of  messages  that  go  to  and 
from  the  brain  is  inconceivably  great.  "When  one  is 
walking,  for  example,  the  mind  continually  sends  a 
multitude  of  messages  to  all  the  muscles  that  together 
perform  this  general  motion  of  the  machinery.  At  the 
same  time  there  are  messages  going  to  the  brain  from 
some  of  the  organs  of  the  senses,  perhaps  from  all  of 
them.  But  the  variety  in  the  messages  is  more  strik- 
ing when  different  motions  are  performed  in  different 
parts  of  the  body.  Observe  one  who  is  playing  on  a 
parlor  organ,  and  at  the  same  time  is  singing.  Mes- 
sages are  sent  in  this  case  to  many  different  parts  for 
different  purposes — to  the  muscles  of  the  foot  that  work 
the  bellows — to  the  muscles  of  the  arm  and  hand  and 
fingers  in  playing  on  the  keys — to  the  muscles  of  the 
eyes  in  moving  them  to  look  at  the  notes — to  the 
muscles  of  the  vocal  ligaments  in  making  the  different 
notes — to  the  muscles  of  the  throat,  lips,  &c.,  in  arti- 
culating the  sounds — and  to  the  muscles  of  the  chest 
in  forcing  out  the  air  through  the  windpipe.  While 
all  this  is  going  on,  the  ear  is  listening  to  discover  if 
there  be  any  error  in  the  sounds,  the  eyes  are  looking 
at  the  notes,  and  the  sense  of  touch  is  guiding  the 
muscles  of  the  hand  in  regulating  the  degree  of  press- 
ure on  the  keys  of  the  organ.  That  is,  while  messages 

What  is  said  of  the  variety  of  messages  that  go  along  the  nerves 
when  one  is  walking  ?  In  what  cases  is  this  variety  most  striking  ? 
Give  the  illustration. 


190  FIRST   BOOK    IN    PHYSIOLOGY. 

are  going  from  the  mind  with  such  rapidity  and  va- 
riety to  the  muscles  of  the  foot,  the  hands,  the  eyes, 
the  throat  and  the  chest,  messages  are  coming  to  the 
mind  from  the  ears,  the  eyes  and  the  fingers.  The 
communications  of  the  mind  with  the  different  parts 
of  the  body  are  in  such  a  case  numerous  and  compli- 
cated beyond  conception. 

24.  I  have  thus  shown  you  how  the  mind  makes 
use  of  its  instruments,  the  organs  of  the  senses  and 
the  muscles.    I  have  spoken  of  them  as  the  machinery 
of  the  mind,  and  you  have  seen  that  these  instruments 
contain  mechanisms  that  are  more  perfect  and  beauti- 
ful than  any  that  man  ever  constructed.     You  have 
seen  that  the  body  is  mostly  a  collection  of  machinery 
for  the  mind  to  use,  and  that  the  purpose  of  those 
parts  which  the  mind  does  not  use  is  to  build  those 
which  it  does  use.     The  object  of  one  portion  of  the 
machinery  of  the  mind,  the  organs  of  the  senses,  is,  as 
you  have  seen,  to  enable  it  to  gain  a  knowledge  of  the 
world  around  it.    The  object  of  the  other  portion  of  its 
machinery,  the  muscles,  with   the   parts   that   they 
move,  is  to  use  this  knowledge  gained  by  the  senses  in 
making  impressions  upon  the  things  and  beings  with 
which  it  is  surrounded.     It  works  with  the  muscles, 
and  with  them  communicates  its  knowledge  to  others. 

25.  This  machinery  of  the  mind  is 'fitted  for  our 
present  state  of  being.     But  this  life  is  short.     This 
body,  with  all  its  ingenious  and  beautiful  contrivances, 
is  to  be  dwelt  in  and  used  by  the  mind  but  a  short 
period  of  time.     In  the  life  which  follows,  its  ever- 

Give  the  summary  in  §24.     "What  is  said  of  the  instruments  which 
the  mind  will  use  in  another  life  ? 


CONNECTION   OF   THE    MIND   AND  BODY.    191 

lasting  life,  it  is  to  have,  as  the  Bible  tells  us,  a  better, 
a  glorified  body.  It  will,  therefore,  have  better  in- 
struments to  use  then  than  it  has  now,  and  so  will  be 
able  both  to  know  more  and  to  do  more  than  it  can 
in  its  present  state. 


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